diff --git a/src/6-math/basic_sqrt_time_algorithms.cpp b/src/6-math/0_sqrt_time_algorithms.hpp
similarity index 52%
rename from src/6-math/basic_sqrt_time_algorithms.cpp
rename to src/6-math/0_sqrt_time_algorithms.hpp
index 4a5149c..9e1b926 100644
--- a/src/6-math/basic_sqrt_time_algorithms.cpp
+++ b/src/6-math/0_sqrt_time_algorithms.hpp
@@ -1,35 +1,32 @@
+#pragma once
 #include "../common/common.hpp"
-
 // 1. Finding Divisors in O(sqrt(x))
 // INPUT: Given a natural number x.
 // OUTPUT: Find all the divisors of x.
 // TIME COMPLEXITY: O(sqrt(x)).
-vector<int> di;
-void findingDivisors(int x) {
-  for (int i = 1; i <= sqrt(x); i++) {
+vector<ll> get_div(ll x) {
+  vector<ll> ret;
+  for (ll i = 1; i * i <= x; i++) {
     if (x % i == 0) {
-      di.push_back(i);
-      if (x / i != i) di.push_back(x / i);
+      ret.push_back(i);
+      if (x / i != i) ret.push_back(x / i);
     }
   }
-  sort(di.begin(), di.end());
+  sort(all(ret));
+  return ret;
 }
-
 // 2. Finding Prime Factorization in O(sqrt(x))
 // INPUT: Given a natural number x.
 // OUTPUT: Find the result of the prime factorization of x.
 // TIME COMPLEXITY: O(sqrt(x)).
-vector<int> p;
-void primeFactorization(int x) {
-  while (x % 2 == 0) {
-    x /= 2;
-    p.push_back(2);
-  }
+vector<ll> factorize(ll x) {
+  vector<ll> ret;
+  while (x % 2 == 0)
+    x /= 2, ret.push_back(2);
   for (int i = 3; i <= sqrt(x); i += 2) {
-    while (x % i == 0) {
-      x /= i;
-      p.push_back(i);
-    }
+    while (x % i == 0)
+      x /= i, ret.push_back(i);
   }
-  if (x > 1) p.push_back(x);
+  if (x > 1) ret.push_back(x);
+  return ret;
 }
\ No newline at end of file
diff --git a/src/6-math/1_modint.hpp b/src/6-math/1_modint.hpp
new file mode 100644
index 0000000..d323362
--- /dev/null
+++ b/src/6-math/1_modint.hpp
@@ -0,0 +1,69 @@
+#pragma once
+#include "../common/common.hpp"
+template <int m>
+class modint {
+  static_assert(m > 0, "Modulus must be positive");
+
+public:
+  static constexpr int mod() { return m; }
+  constexpr modint(ll y = 0) : x(y >= 0 ? y % m : (y % m + m) % m) {}
+  constexpr int val() const { return x; }
+  constexpr modint &operator+=(const modint &r) {
+    if ((x += r.x) >= m) x -= m;
+    return *this;
+  }
+  constexpr modint &operator-=(const modint &r) {
+    if ((x += m - r.x) >= m) x -= m;
+    return *this;
+  }
+  constexpr modint &operator*=(const modint &r) {
+    x = static_cast<int>(1LL * x * r.x % m);
+    return *this;
+  }
+  constexpr modint &operator/=(const modint &r) { return *this *= r.inv(); }
+  constexpr bool operator==(const modint &r) const { return x == r.x; }
+  constexpr modint operator+() const { return *this; }
+  constexpr modint operator-() const { return modint{-x}; }
+  constexpr friend modint operator+(const modint &l, const modint &r) {
+    return modint{l} += r;
+  }
+  constexpr friend modint operator-(const modint &l, const modint &r) {
+    return modint{l} -= r;
+  }
+  constexpr friend modint operator*(const modint &l, const modint &r) {
+    return modint{l} *= r;
+  }
+  constexpr friend modint operator/(const modint &l, const modint &r) {
+    return modint{l} /= r;
+  }
+  constexpr modint inv() const {
+    int a = x, b = m, u = 1, v = 0;
+    while (b > 0) {
+      int t = a / b;
+      swap(a -= t * b, b);
+      swap(u -= t * v, v);
+    }
+    return modint{u};
+  }
+  constexpr modint pow(ll n) const {
+    modint ret(1), mul(x);
+    while (n > 0) {
+      if (n & 1) ret *= mul;
+      mul *= mul;
+      n >>= 1;
+    }
+    return ret;
+  }
+  friend ostream &operator<<(ostream &os, const modint &r) {
+    return os << r.x;
+  }
+  friend istream &operator>>(istream &is, modint &r) {
+    ll t;
+    is >> t;
+    r = modint{t};
+    return is;
+  }
+
+private:
+  int x;
+};
diff --git a/src/6-math/euclidean_algorithms.cpp b/src/6-math/2_extgcd.hpp
similarity index 81%
rename from src/6-math/euclidean_algorithms.cpp
rename to src/6-math/2_extgcd.hpp
index daf9354..862d713 100644
--- a/src/6-math/euclidean_algorithms.cpp
+++ b/src/6-math/2_extgcd.hpp
@@ -1,3 +1,4 @@
+#pragma once
 #include "../common/common.hpp"
 
 // GCD, LCM
@@ -40,8 +41,6 @@ ll lcm(ll a, ll b) {
 
 // TIME COMPLEXITY: O(log(AB))
 
-// BOJ 14565 AC Code
-// https://www.acmicpc.net/problem/14565
 pair<pll, ll> egcd(ll a, ll b) {
   ll s = 0, olds = 1;
   ll t = 1, oldt = 0;
@@ -59,21 +58,22 @@ pair<pll, ll> egcd(ll a, ll b) {
   // oldr = gcd(a, b)
   return {{olds, oldt}, oldr};
 }
-ll linearCongruence(ll a, ll b, ll n) { // Find x such that ax = b (mod n).
+ll linear_congruence(ll a, ll b, ll n) { // Find x such that ax = b (mod n).
   pair<pll, ll> res = egcd(a, n);
   ll g = res.sc;
   // ax + ny = b has a solution iff gcd(a,n) | b.
   if (b % g) return -1;
   return (res.fr.fr * (b / g) % n + n) % n;
 }
-ll modInv(ll a, ll p) { // Find x such that ax = 1 (mod p).
-  pair<pll, ll> res = egcd(a, p);
-  // Modular inverse exists iff gcd(a, p) = 1.
-  if (res.sc == 1) return (res.fr.fr + p) % p;
-  else return -1;
+ll inv_mod(ll a, ll p) { // Find x such that ax = 1 (mod p).
+  ll b = p, u = 1, v = 0;
+  while (b) {
+    ll t = a / b;
+    a -= t * b;
+    swap(a, b);
+    u -= t * v;
+    swap(u, v);
+  }
+  if (u < 0) u += p;
+  return u;
 }
-int main() {
-  ll N, A;
-  cin >> N >> A;
-  cout << N - A << ' ' << modInv(A, N);
-}
\ No newline at end of file
diff --git a/src/6-math/3_ntt.hpp b/src/6-math/3_ntt.hpp
new file mode 100644
index 0000000..53a67b4
--- /dev/null
+++ b/src/6-math/3_ntt.hpp
@@ -0,0 +1,111 @@
+#pragma once
+#include "../common/common.hpp"
+#include "1_modint.hpp"
+#include "2_extgcd.hpp"
+constexpr int get_primitive_root(int mod) {
+  if (mod == 167772161) return 3;
+  if (mod == 469762049) return 3;
+  if (mod == 754974721) return 11;
+  if (mod == 998244353) return 3;
+  if (mod == 1224736769) return 3;
+}
+template <typename mint>
+void ntt(vector<mint> &a) {
+  constexpr int mod = mint::mod();
+  constexpr mint primitive_root = get_primitive_root(mod);
+
+  const int n = sz(a);
+  for (int m = n; m > 1; m >>= 1) {
+    mint omega = primitive_root.pow((mod - 1) / m);
+    for (int s = 0; s < n / m; ++s) {
+      mint w = 1;
+      for (int i = 0; i < m / 2; ++i) {
+        mint l = a[s * m + i];
+        mint r = a[s * m + i + m / 2];
+        a[s * m + i] = l + r;
+        a[s * m + i + m / 2] = (l - r) * w;
+        w *= omega;
+      }
+    }
+  }
+}
+template <typename mint>
+void intt(vector<mint> &a) {
+  constexpr int mod = mint::mod();
+  constexpr mint primitive_root = get_primitive_root(mod);
+
+  const int n = sz(a);
+  for (int m = 2; m <= n; m <<= 1) {
+    mint omega = primitive_root.pow((mod - 1) / m).inv();
+    for (int s = 0; s < n / m; ++s) {
+      mint w = 1;
+      for (int i = 0; i < m / 2; ++i) {
+        mint l = a[s * m + i];
+        mint r = a[s * m + i + m / 2] * w;
+        a[s * m + i] = l + r;
+        a[s * m + i + m / 2] = l - r;
+        w *= omega;
+      }
+    }
+  }
+}
+template <typename mint>
+vector<mint> convolution(vector<mint> a, vector<mint> b) {
+  const int size = sz(a) + sz(b) - 1;
+  int n = 1;
+  while (n < size) n <<= 1;
+  a.resize(n), b.resize(n);
+  ntt(a), ntt(b);
+  for (int i = 0; i < n; ++i) a[i] *= b[i];
+  intt(a);
+  a.resize(size);
+  mint n_inv = mint(n).inv();
+  for (int i = 0; i < size; ++i) a[i] *= n_inv;
+  return a;
+}
+vector<ll> convolution_ll(const vector<ll> &a,
+                          const vector<ll> &b) {
+  static constexpr ll m0 = 167772161;
+  static constexpr ll m1 = 469762049;
+  static constexpr ll m2 = 754974721;
+  static constexpr ll m01 = m0 * m1;
+  static constexpr __int128_t m012 = (__int128_t)m01 * m2;
+
+  static const ll inv_m0_mod_m1 = inv_mod(m0 % m1, m1);
+  static const ll inv_m01_mod_m2 = inv_mod(m01 % m2, m2);
+
+  using mint0 = modint<m0>;
+  using mint1 = modint<m1>;
+  using mint2 = modint<m2>;
+
+  vector<mint0> a0(all(a)), b0(all(b));
+  vector<mint1> a1(all(a)), b1(all(b));
+  vector<mint2> a2(all(a)), b2(all(b));
+
+  auto c0 = convolution(a0, b0);
+  auto c1 = convolution(a1, b1);
+  auto c2 = convolution(a2, b2);
+
+  vector<ll> c(sz(c0));
+  for (int i = 0; i < sz(c1); ++i) {
+    ll r0 = c0[i].val();
+    ll r1 = c1[i].val();
+    ll r2 = c2[i].val();
+
+    ll t1 = (r1 - r0) % m1;
+    if (t1 < 0) t1 += m1;
+    ll k1 = (ll)((__int128_t)t1 * inv_m0_mod_m1 % m1);
+    __int128_t x01 = r0 + (__int128_t)m0 * k1;
+
+    ll x01_mod_m2 = (ll)(x01 % m2);
+    ll t2 = (r2 - x01_mod_m2) % m2;
+    if (t2 < 0) t2 += m2;
+    ll k2 = (ll)((__int128_t)t2 * inv_m01_mod_m2 % m2);
+    __int128_t x = x01 + (__int128_t)m01 * k2;
+
+    if (x >= m012 / 2) x -= m012;
+
+    c[i] = (ll)x;
+  }
+  return c;
+}
diff --git a/src/6-math/fft.cpp b/src/6-math/4_fft.hpp
similarity index 62%
rename from src/6-math/fft.cpp
rename to src/6-math/4_fft.hpp
index 7c75d35..4e2800d 100644
--- a/src/6-math/fft.cpp
+++ b/src/6-math/4_fft.hpp
@@ -77,48 +77,3 @@ vector<ll> multiply_mod(const vector<ll> &a, const vector<ll> &b, const ull mod)
   return ret;
 }
 } // namespace fft
-namespace ntt {
-constexpr ll MOD = (119 << 23) + 1, root = 3; // = 998244353
-// For p < 2^30 there is also e.g. 5 << 25, 7 << 26, 479 << 21
-// and 483 << 21 (same root). The last two are > 10^9.
-ll modpow(ll b, ll e) {
-  ll ans = 1;
-  for (; e; b = b * b % MOD, e /= 2)
-    if (e & 1) ans = ans * b % MOD;
-  return ans;
-}
-void ntt(vector<ll> &a) {
-  int n = sz(a), L = 31 - __builtin_clz(n);
-  static vector<ll> rt(2, 1);
-  for (static int k = 2, s = 2; k < n; k *= 2, s++) {
-    rt.resize(n);
-    ll z[] = {1, modpow(root, MOD >> s)};
-    for (int i = k; i < 2 * k; i++)
-      rt[i] = rt[i / 2] * z[i & 1] % MOD;
-  }
-  vector<ll> rev(n);
-  for (int i = 0; i < n; i++) rev[i] = (rev[i / 2] | (i & 1) << L) / 2;
-  for (int i = 0; i < n; i++)
-    if (i < rev[i]) swap(a[i], a[rev[i]]);
-  for (int k = 1; k < n; k *= 2)
-    for (int i = 0; i < n; i += 2 * k)
-      for (int j = 0; j < k; j++) {
-        ll z = rt[j + k] * a[i + j + k] % MOD, &ai = a[i + j];
-        a[i + j + k] = ai - z + (z > ai ? MOD : 0);
-        ai += (ai + z >= MOD ? z - MOD : z);
-      }
-}
-vector<ll> multiply(const vector<ll> &a, const vector<ll> &b) {
-  if (a.empty() || b.empty()) return {};
-  int s = sz(a) + sz(b) - 1, B = 32 - __builtin_clz(s),
-      n = 1 << B;
-  int inv = modpow(n, MOD - 2);
-  vector<ll> L(a), R(b), out(n);
-  L.resize(n), R.resize(n);
-  ntt(L), ntt(R);
-  for (int i = 0; i < n; i++)
-    out[-i & (n - 1)] = (ll)L[i] * R[i] % MOD * inv % MOD;
-  ntt(out);
-  return {out.begin(), out.begin() + s};
-}
-} // namespace ntt
\ No newline at end of file
diff --git a/src/6-math/5_sieve.hpp b/src/6-math/5_sieve.hpp
new file mode 100644
index 0000000..b964411
--- /dev/null
+++ b/src/6-math/5_sieve.hpp
@@ -0,0 +1,47 @@
+#pragma once
+#include "../common/common.hpp"
+// 1. Sieve of Eratosthenes
+// TIME COMPLEXITY: O(Nlog(log(N)))
+namespace sieve {
+constexpr int N = 1010101;
+bool is_prime[N];
+vector<int> prime(1, 2);
+void get_prime() {
+  fill(is_prime + 2, is_prime + N, 1);
+  for (ll i = 4; i < N; i += 2)
+    is_prime[i] = 0;
+  for (ll i = 3; i < N; i += 2) {
+    if (!is_prime[i]) continue;
+    prime.push_back(i);
+    for (ll j = i * i; j < N; j += i * 2)
+      is_prime[j] = 0;
+  }
+}
+}; // namespace sieve
+// 2. Linear Sieve
+namespace linear_sieve {
+constexpr int N = 5050505;
+vector<int> sp(N);
+vector<ll> prime;
+void linear_sieve() { // Determine prime numbers between 1 and MAXN in O(MAXN)
+  for (int i = 2; i < N; i++) {
+    if (!sp[i]) {
+      prime.push_back(i);
+      sp[i] = i;
+    }
+    for (auto j : prime) {
+      if (i * j >= N) break;
+      sp[i * j] = j;
+      if (i % j == 0) break;
+    }
+  }
+}
+vector<int> factorize(int x) { // factorization in O(log x)
+  vector<int> ret;
+  while (x > 1) {
+    ret.push_back(sp[x]);
+    x /= sp[x];
+  }
+  return ret;
+}
+}; // namespace linear_sieve
diff --git a/src/6-math/6_binom.hpp b/src/6-math/6_binom.hpp
new file mode 100644
index 0000000..c1452c1
--- /dev/null
+++ b/src/6-math/6_binom.hpp
@@ -0,0 +1,21 @@
+#pragma once
+#include "../common/common.hpp"
+namespace binom {
+// nCr mod p in O(1)
+constexpr int MOD = 1e9 + 7;
+constexpr int N = 4040404;
+ll fac[N], inv[N], facInv[N];
+void build() { // You must run build() before you call binom(int n, int r).
+  fac[0] = fac[1] = inv[1] = 1;
+  facInv[0] = facInv[1] = 1;
+  for (int i = 2; i < N; i++) {
+    fac[i] = i * fac[i - 1] % MOD;
+    inv[i] = -(MOD / i) * inv[MOD % i] % MOD;
+    if (inv[i] < 0) inv[i] += MOD;
+    facInv[i] = facInv[i - 1] * inv[i] % MOD;
+  }
+}
+ll binom(int n, int r) {
+  return fac[n] * facInv[r] % MOD * facInv[n - r] % MOD;
+}
+}; // namespace binom
diff --git a/src/6-math/binomial_coefficient.cpp b/src/6-math/binomial_coefficient.cpp
deleted file mode 100644
index ba7eee0..0000000
--- a/src/6-math/binomial_coefficient.cpp
+++ /dev/null
@@ -1,58 +0,0 @@
-#include "../common/common.hpp"
-
-// nCr in O(r)
-// Beware of integer overflow
-ll binom(int n, int r) {
-  if (r < 0 || n < r) return 0;
-  r = min(r, n - r);
-  ll ret = 1;
-  for (ll i = 1; i <= r; i++) {
-    ret *= n + 1 - i;
-    ret /= i;
-  }
-  return ret;
-}
-// nCr (Pascal’s Rule)
-ll binomDP[1010][1010];
-void init() {
-  for (int i = 0; i < 1010; i++) {
-    for (int j = 0; j < 1010; j++) {
-      binomDP[i][j] = -1;
-    }
-  }
-}
-ll binom(int n, int r) {
-  if (r < 0 || n < r) return 0;
-  ll &ret = binomDP[n][r];
-  if (ret != -1) return ret;
-  if (n == 1) return ret = 1;
-  return binom(n - 1, r - 1) + binom(n - 1, r);
-}
-// nCr mod p in O(1)
-const int MOD = 1e9 + 7;
-const int MAXN = 4040404;
-ll fac[MAXN], inv[MAXN], facInv[MAXN];
-ll binom(int n, int r) {
-  return fac[n] * facInv[r] % MOD * facInv[n - r] % MOD;
-}
-int main() {
-  cin.tie(NULL), cout.tie(NULL);
-  ios_base::sync_with_stdio(false);
-  // Preprocessing in O(N)
-  fac[0] = fac[1] = inv[1] = 1;
-  facInv[0] = facInv[1] = 1;
-  for (int i = 2; i < MAXN; i++) {
-    fac[i] = i * fac[i - 1] % MOD;
-    inv[i] = -(MOD / i) * inv[MOD % i] % MOD;
-    if (inv[i] < 0) inv[i] += MOD;
-    facInv[i] = facInv[i - 1] * inv[i] % MOD;
-  }
-  // Answer each query in O(1)
-  int q;
-  cin >> q;
-  while (q--) {
-    int n, r;
-    cin >> n >> r;
-    cout << binom(n, r) << '\n';
-  }
-}
\ No newline at end of file
diff --git a/src/6-math/sieve.cpp b/src/6-math/sieve.cpp
deleted file mode 100644
index c96bf79..0000000
--- a/src/6-math/sieve.cpp
+++ /dev/null
@@ -1,55 +0,0 @@
-#include "../common/common.hpp"
-
-// Sieve of Eratosthenes
-// TIME COMPLEXITY: O(Nlog(log(N)))
-const int MAX = 1e6;
-bool isPrime[MAX + 1];
-vector<int> prime(1, 2);
-void getPrime() {
-  fill(isPrime + 2, isPrime + MAX + 1, 1);
-  for (ll i = 4; i <= MAX; i += 2)
-    isPrime[i] = 0;
-  for (ll i = 3; i <= MAX; i += 2) {
-    if (!isPrime[i]) continue;
-    prime.push_back(i);
-    for (ll j = i * i; j <= MAX; j += i * 2)
-      isPrime[j] = 0;
-  }
-}
-
-// Linear Sieve
-const int MAXN = 5000000;
-vector<int> sp(MAXN + 1);
-vector<ll> prime;
-// Determine prime numbers between 1 and MAXN in O(MAXN)
-void linearSieve() {
-  for (int i = 2; i <= MAXN; i++) {
-    if (!sp[i]) {
-      prime.push_back(i);
-      sp[i] = i;
-    }
-    for (auto j : prime) {
-      if (i * j > MAXN) break;
-      sp[i * j] = j;
-      if (i % j == 0) break;
-    }
-  }
-}
-// factorization in O(log x)
-void factorization(int x) {
-  while (x > 1) {
-    cout << sp[x] << ' ';
-    x /= sp[x];
-  }
-  cout << '\n';
-}
-int main() {
-  linearSieve();
-  int n;
-  cin >> n;
-  while (n--) {
-    int x;
-    cin >> x;
-    factorization(x);
-  }
-}
\ No newline at end of file