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

fac = [0] * (N + 1)
fac[0] = 1
for i in range(N):
    fac[i + 1] = fac[i] * (i + 1) % 1000000007

def mcomb(n, k):
    if n == 0 and k == 0:
        return 1
    if n < k or k < 0:
        return 0
    return fac[n] * pow(fac[n - k], 1000000005, 1000000007) * pow(fac[k], 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)