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