#include <bits/stdc++.h>
#include <atcoder/all>
using mint = atcoder::modint1000000007;
using namespace std;
const int MAX = 510000;
const int MOD = 1000000007;

mint fac[MAX], finv[MAX], inv[MAX];

void COMinit() {
	fac[0] = fac[1] = 1;
	finv[0] = finv[1] = 1;
	inv[1] = 1;
	for (int i = 2; i < MAX; i++){
		fac[i] = fac[i - 1] * i;
		inv[i] = MOD - inv[MOD%i] * (MOD / i);
		finv[i] = finv[i - 1] * inv[i];
	}
}

mint COM(int n, int k){
	if (n < k) return 0;
	if (n < 0 || k < 0) return 0;
	return fac[n] * finv[k] * finv[n - k];
}

int main() {
	int n, m;
	cin >> n >> m;
	COMinit();
	vector<mint> f(n + 1);
	for (int i = 1; i <= m; i++){
		f[i] = COM(m, i) * (mint(i)).pow(n) - f[i - 1];
	}
	cout << f[m].val() << endl;
}