#define ll long long
#define P 1000000007
ll n,s,t;m,i;
ll pom(ll a,ll i,ll m){return i?i%2?pom(a*a%m,i/2,m)*a%m:pom(a*a%m,i/2,m)%m:1;}
main(){
	scanf("%lld%d",&n,&m);
	s=pom(m,n,P);
	t=1;
	for(i=1;i<m;i++)s+=(i%2?-1:1)*(t=t*(m-i+1)%P*pom(i,P-2,P)%P)*pom(m-i,n,P)%P+P;
	s=!printf("%d",s%P);
}