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 
X=1 
for i in range(M):
    P,X=P+X*pow(M-i,N,z)*c(M,M-i),-X 
print(P%z)