p = 10**9+7
def my_pow(b,e):
	ret = 1
	while e:
		if e&1: ret = ret * b % p
		b = b * b % p
		e>>=1
	return ret 
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] = my_pow(F[M],p-2)
for i in xrange(M,0,-1):FI[i-1] = i*FI[i]%p
print sum(F[M]*FI[k]*FI[M-k]*my_pow(M-k,N)*((-1)**(k%2)) for k in xrange(M))%p