import sys
sys.setrecursionlimit(10**8)

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)

def f(x):
    if x == 0:
        return 0
    return (cmb(M, x) * pow(x, N, p) - f(x - 1))%p

ans = f(M)
print(ans)