p = 10**9+7
N,M = map(int,raw_input().split())
F = [1]; FI = [0]*(M+1)
for i in xrange(1,M+1):F += [i*F[i-1]%p]
FI[M] = pow(F[M],p-2,p)
for i in xrange(M,0,-1):FI[i-1] = i*FI[i]%p
print sum(F[M]*FI[k]*FI[M-k]*pow(M-k,N,p)*((-1)**(k%2)) for k in xrange(M))%p