N,M=map(int,input().split())
z,g=10**9+7,[1,1]
d=range
for i in d(2,N+1):g.append(g[-1]*i%z)
print(sum((-1)**i*pow(M-i,N,z)*g[M]*pow(g[i]*g[M-i],z-2,z)for i in d(M))%z)