import sys
readline = sys.stdin.readline
MOD = 10**9+7
def frac(limit):
    frac = [1]*limit
    for i in range(2,limit):
        frac[i] = i * frac[i-1]%MOD
    fraci = [None]*limit
    fraci[-1] = pow(frac[-1], MOD -2, MOD)
    for i in range(-2, -limit-1, -1):
        fraci[i] = fraci[i+1] * (limit + i + 1) % MOD
    return frac, fraci
def comb(a, b):
    if not a >= b >= 0:
        return 0
    return frac[a]*fraci[b]*fraci[a-b]%MOD
frac, fraci = frac(1341398)

N, M = map(int, readline().split())
ans = pow(M, N, MOD)
for k in range(1, M):
    ans = (ans + (-1)**k * comb(M, k) * pow(M-k, N, MOD))
print(ans % MOD)