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

fac = [0] * (M + 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 = 0
for i in range(1, M + 1):
    result = mcomb(M, i) * pow(i, N, 1000000007) - result
    result %= 1000000007

print(result)