#include <iostream>
using namespace std;

#define LL long long
#define MOD 1000000007
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)   FOR(i,0,n)

LL pow(LL n, LL m){
  LL a = 1;
  LL i,prod;
  prod=n;
  while(m > 0){
    if(m % 2 == 1)
      a = a*prod % MOD;
    prod = prod*prod %MOD;
    m /= 2;
  }
  return a;
}

LL ans(LL n, LL m){
  LL val = pow(m,n);
  LL i;
  LL com = 1;
  FOR(i,1,m){
    com = (com*(m-i+1)/i) % MOD;
    val = (m-i)%2==0 ? (val + com*pow(i,n)) % MOD : (MOD + (val - com*pow(i,n)) % MOD) % MOD;
  }
  return val;
}

int main(){
  LL n,m;
  cin >> n >> m;
  cout << ans(n,m) << endl;
  return 0;
}