#include <bits/stdc++.h>
using namespace std;

const int MAXK = int(1e6);
const int MOD = int(1e9) + 7;

int int_pow(int v, int p) {
  int res = not(v == 0 and p);
  while (p) {
    if (p & 1) {
      res = 1LL * res * v % MOD;
    }
    p >>= 1;
    v = 1LL * v * v % MOD;
  }
  return res;
}

int inv(int v) { return int_pow(v, MOD - 2); }

int fact[MAXK + 1 + 1];

int64_t N;
int K;

int f[MAXK + 2 + 1];

signed main() {
  ios::sync_with_stdio(0);
  cin >> N >> K;
  for (int i = fact[0] = 1; i <= K + 1; ++i) {
    fact[i] = 1LL * fact[i - 1] * i % MOD;
  }
  for (int i = 1; i <= K + 2; ++i) {
    f[i] = (f[i - 1] + int_pow(i, K)) % MOD;
  }
  if (N <= K + 2) {
    cout << f[N] << endl;
  } else {
    int xmj = 1;
    for (int i = 1; i <= K + 2; ++i) {
      xmj = 1LL * xmj * (N % MOD - i) % MOD;
    }
    int ans = 0;
    for (int i = 1; i <= K + 2; ++i) {
      int p = 1LL * f[i] * xmj % MOD * inv(N % MOD - i) % MOD *
              inv(1LL * fact[i - 1] * fact[K + 2 - i] % MOD) % MOD;
      if (K + 2 - i & 1) p *= -1;
      (ans += p) %= MOD;
    }
    if (ans < 0) ans += MOD;
    cout << ans << endl;
  }
  return 0;
}