#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 100010,mod = 1e9+7;
int qmi(int a,int k,int p){
    int res = 1;
    while(k){
        if(k&1) res = res * a % p;
        a = a * a %p;
        k >>= 1;
    }
    return res;
}
int fact[N],infact[N];

int c(int n,int m){
    if(n<0||m>n||m<0) return 0;
    return fact[n] * infact[n-m]%mod * infact[m] % mod;
}
int s2(int n,int m){
    int ans = 0;
    for(int k=0;k<=m;k++){
        if(k%2){
            ans=(ans-c(m,k) % mod * qmi(m-k,n,mod) + mod)% mod;
        }else{
            ans=(ans + c(m,k) %mod * qmi(m-k,n,mod) )% mod;
        }
    }
    return ans*infact[m]%mod;
}
signed main(){

    int n,m;
    cin>>n>>m;
    fact[0]=1,infact[0]=1;
	///就是这里，把n该成N就不对了为什么？？
	for(int i=1;i<=n;i++){
        fact[i] = (fact[i-1]*i %mod);
        infact[i]=(infact[i-1]*qmi(i,mod-2,mod))%mod;
    }
    int ans = s2(n,m);
    cout<<ans<<'\n';
}