ACM模版
#include <iostream>
using namespace std;
typedef long long ll;
const int MAXN = 1e6 + 10;
const int MOD = 1e9 + 7;
int n, m;
ll fac[MAXN]; // 阶乘
ll inv[MAXN]; // 阶乘的逆元
ll QPow(ll x, ll n)
{
ll ret = 1;
ll tmp = x % MOD;
while (n)
{
if (n & 1)
{
ret = (ret * tmp) % MOD;
}
tmp = tmp * tmp % MOD;
n >>= 1;
}
return ret;
}
void init()
{
fac[0] = 1;
for (int i = 1; i < MAXN; i++)
{
fac[i] = fac[i - 1] * i % MOD;
}
inv[MAXN - 1] = QPow(fac[MAXN - 1], MOD - 2);
for (int i = MAXN - 2; i >= 0; i--)
{
inv[i] = inv[i + 1] * (i + 1) % MOD;
}
}
ll C(ll a, ll b)
{
if (b > a)
{
return 0;
}
if (b == 0)
{
return 1;
}
return fac[a] * inv[b] % MOD * inv[a - b] % MOD;
}
int main()
{
init();
cin >> n >> m;
ll ans = 0;
for (int i = 0, e = 1; i <= m; i++, e *= -1)
{
ans += C(m, i) * QPow(m - i, n) % MOD * e;
ans %= MOD;
}
cout << (ans + MOD) % MOD << endl;
return 0;
}