/** * @FileName f.cpp * @Author kanpurin * @Created 2020.05.13 19:23:36 **/ #include "bits/stdc++.h" using namespace std; typedef long long ll; constexpr int MOD = 1e9 + 7; struct mint { private: long long x; public: mint(long long x = 0) :x((MOD+x)%MOD) {} mint(std::string &s) { long long z = 0; for (int i = 0; i < s.size(); i++) { z *= 10; z += s[i] - '0'; z %= MOD; } this->x = z; } mint& operator+=(const mint &a) { if ((x += a.x) >= MOD) x -= MOD; return *this; } mint& operator-=(const mint &a) { if ((x += MOD - a.x) >= MOD) x -= MOD; return *this; } mint& operator*=(const mint &a) { (x *= a.x) %= MOD; return *this; } mint& operator/=(const mint &a) { long long n = MOD - 2; mint u = 1, b = a; while (n > 0) { if (n & 1) { u *= b; } b *= b; n >>= 1; } return *this *= u; } mint operator+(const mint &a) const { mint res(*this); return res += a; } mint operator-(const mint &a) const { mint res(*this); return res -= a; } mint operator*(const mint &a) const { mint res(*this); return res *= a; } mint operator/(const mint &a) const { mint res(*this); return res /= a; } friend std::ostream& operator<<(std::ostream &os, const mint &n) { return os << n.x; } bool operator==(const mint &a) const { return this->x == a.x; } }; //pow template T pow(T k, U n, T unity = 1) { while (n > 0) { if (n & 1) { unity *= k; } k *= k; n >>= 1; } return unity; } // comb (前計算O(NlogMOD) クエリO(1)) struct Combination { private: int N; vector< mint > FACT, IFACT; // pow mint pow(mint k, ll n) { mint res = 1; while (n > 0) { if (n & 1) { res *= k; } k *= k; n >>= 1; } return res; } public: // nCk Combination(int n) : N(n) { FACT.resize(n + 1); IFACT.resize(n + 1); FACT[0] = 1; IFACT[0] = 1; for (int i = 1; i <= n; i++) { FACT[i] = FACT[i - 1] * i; IFACT[i] = pow(FACT[i], MOD - 2); } } mint comb(int n, int r) { if (n < 0 || r < 0 || r > n) return 0; if (r > n / 2) r = n - r; return FACT[n] * IFACT[n - r] * IFACT[r]; } }; int main() { int n,m;cin >> n >> m; mint ans = 0; Combination cb(m); for (int i = 1; i <= m; i++) { ans += cb.comb(m,i) * pow(mint(i),n) * (((m-i) & 1) ? (-1) : 1); } cout << ans << endl; return 0; }