n,m=map(int,raw_input().split())
M=10**9+7
I=[1,1];F=[1,1];R=[1,1]
for i in range(2,m+1):
	I+=[(M-M//i)*I[M%i]%M]
	F+=[i*F[i-1]%M]
	R+=[I[i]*R[i-1]%M]
print sum((-1)**k*F[m]*R[k]*R[m-k]*pow(m-k,n,M)for k in range(m))%M