/*
Sample solution to landoftrees problem in NCPC2018 by Andreas Björklund
Evaluation of inclusion-exclusion formula 
sum_{i=2)^k (-1)^{k-i}(k choose i)(i-1)^{n-1}i.
*/

#include <stdio.h>

#define MOD (1000000007)
int n,k;

int modexp(int a,int b, int c)
{
    if (b==0) return 1;
    long long tmp = modexp(a,b/2,c);
    tmp = (tmp * tmp) % c;
    if ((b%2)==1) tmp = (tmp * a) % c;
    return (int)tmp;
}

int main()
{
    int i;
    long long sum = 0;
    long long talj, namn;
    scanf("%d %d",&n,&k);
    talj = k;
    namn = 1;
    for (i=2;i<=k;i++) {
        long long tmp = modexp(i-1,n-1,MOD);
        tmp = (tmp * i) % MOD;
        talj = (talj * (k-i+1)) % MOD;
        namn = (namn * modexp(i,MOD-2,MOD)) % MOD;
        tmp = (tmp * talj) % MOD;
        tmp = (tmp * namn) % MOD;
        if ((k-i) % 2 == 1) tmp = MOD-tmp;
        sum = (sum + tmp) % MOD;
    }
    printf("%lld\n", sum);
    return 0;
}