n,m=map(int,input().split())
M=10**9+7
fa=[1,1]
fb=[1,1]
for i in range(2,n+1):
  fa+=[fa[-1]*i%M]
  fb+=[fb[-1]*(M//i)*fb[M%i]*fa[M%i-1]*(-1)%M]
c=lambda n,k:fa[n]*fb[k]*fb[n-k]%M if n>=k else 0
a=0
for i in range(m+1):
  a+=c(m,i)*pow(m-i,n,M)*((-1)**(i%2))
  a%=M
print(a)