p = 10**9+7
N, M = map(int, input().split())

def cmb(n, r):
    if (r < 0) or (n < r):
        return 0
    r = min(r, n - r)
    return fact[n] * factinv[r] * factinv[n-r] % p

fact = [1, 1]  # fact[n] = (n! mod p)
factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
inv = [0, 1]  # factinv 計算用

for i in range(2, N + 1):
    fact.append((fact[-1] * i) % p)
    inv.append((-inv[p % i] * (p // i)) % p)
    factinv.append((factinv[-1] * inv[-1]) % p)

ans = 0
for i in range(M):
    # M choose (M - i) * (M - i)**N
    if i%2 == 0:
        ans += (cmb(M, M - i) * pow(M - i, N, p)) % p
    else:
        ans -= (cmb(M, M - i) * pow(M - i, N, p)) % p
    ans %= p

print(ans)