z=10**9+7
N,M=map(int,input().split())
g=[1,1]
h=[1,1]
v=[0,1]
d=range
for i in d(2,N+1):
  g.append(g[-1]*i%z)
  v.append(-v[z%i]*(z//i)%z)
  h.append(h[-1]*v[-1]%z)
print(sum(pow(-1,i)*pow(M-i,N,z)*g[M]*h[i]*h[M-i] for i in d(M))%z)