#include <bits/stdc++.h>
using namespace std;
const long m = 1000000007;
const long p = 500000006;
int a, b;
long dp[5001][5001];

long mpow(long b, long e) {
  if (e == 0) return 1;
  if (e % 2 == 1) return b * mpow(b, e - 1) % m;
  long t = mpow(b, e / 2);
  return t * t % m;
}

int main() {
  cin >> a >> b;
  
  dp[0][0] = 1;
  for (int i = 0; i < a; ++i) {
    for (int j = 0; j <= i; ++j) {
      (dp[i + 1][j + 1] += dp[i][j]) %= m;
      (dp[i + 1][j] += j * dp[i][j]) %= m;
    }
  }
  
  long f = 1;
  long sum = 0;
  for (int j = 0; j <= a; ++j) {
    long l = dp[a][j] * f % m;
    long r = mpow(p - j, b);
    (sum += l * r) %= m;
    f = f * (p - j) % m;
  }
  cout << sum << endl;
}