from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

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

class combination():
    
    def __init__(self,N,p):
        
        
        self.fact = [1, 1]  # fact[n] = (n! mod p)
        self.factinv = [1, 1]  # factinv[n] = ((n!)^(-1) mod p)
        self.inv = [0, 1]  # factinv 計算用
        self.p = p
        
        for i in range(2, N + 1):
            self.fact.append((self.fact[-1] * i) % p)
            self.inv.append((-self.inv[p % i] * (p // i)) % p)
            self.factinv.append((self.factinv[-1] * self.inv[-1]) % p)
        

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

C = combination(M+1,mod)

ans = pow(M,N,mod)
for i in range(1,M):
    
    if i%2:
        ans -= C.cmb(M,i)*pow(M-i,N,mod)
    else:
        ans += C.cmb(M,i)*pow(M-i,N,mod)
    ans %= mod
print(ans)