N,M = map(int,input().split())

P = 10 ** 9 + 7
C = N + 5
fact = [1] * C
fact_inv = [1] * C
for i in range(2,C):
    fact[i] = fact[i-1] * i % P
fact_inv[-1] = pow(fact[-1],P-2,P)
for i in range(C-2,1,-1):
    fact_inv[i] = fact_inv[i+1] * (i+1) % P
def comb(n,k):
    return fact[n] * fact_inv[k] % P * fact_inv[n-k] % P
ans = pow(M,N,P)
for i in range(1,M):
    if i % 2 == 1:
        c = -1
    else:
        c = 1
    tmp = comb(M,M-i) * pow(M-i,N,P) % P
    ans = (ans + c * tmp) % P
print(ans)