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

def mcomb(n, k):
    a = 1
    b = 1
    for i in range(k):
        a *= n - i
        a %= 1000000007
        b *= i + 1
        b %= 1000000007
    return a * pow(b, 1000000005, 1000000007) % 1000000007

result = pow(M, N, 1000000007)
for i in range(1, M):
    result -= pow(i, N, 1000000007) * mcomb(N, i)
    result %= 1000000007
print(result)