#pragma GCC optimize "O3"
#pragma GCC target "tune=native"
#pragma GCC target "avx"
#define NDEBUG 1
#include <bits/stdc++.h>

using namespace std;
using ll = long long;

constexpr ll MOD = 1000000007LL;

constexpr int MAX = 10000;
int K;
ll ys[MAX + 2];

ll power(const ll p, const int n)
{
    if (n == 0) {
        return 1;
    }
    if (n % 2 == 1) {
        return power(p, n - 1) * p % MOD;
    } else {
        const ll pp = power(p, n / 2);
        return pp * pp % MOD;
    }
}

inline ll inverse(const ll p)
{
    return power(p, MOD - 2);
}

inline ll minu(const ll a, const ll b) { return (a >= b ? a - b : a + MOD - b); }

inline ll LagrangeInterpolation(const ll x)
{
    ll n = 1;
    for (ll i = 0; i <= K + 1; i++) {
        (n *= x - i) %= MOD;
    }
    ll ans = 0;
    for (ll i = 0; i <= K + 1; i++) {
        ll d = 1;
        for (ll j = 0; j <= K + 1; j++) {
            if (i == j) {
                continue;
            }
            (d *= minu(i, j)) %= MOD;
        }
        (ans += (n * inverse(x - i) % MOD) * (inverse(d) * ys[i] % MOD) % MOD) %= MOD;
    }
    return ans;
}

int main()
{
    ll N;
    cin >> N >> K;
    N %= MOD;
    if (N == 0) {
        cout << 0 << endl;
    } else {
        for (int i = 1; i <= K + 1; i++) {
            ys[i] = (ys[i - 1] + power(i, K)) % MOD;
            if (i == N) {
                cout << ys[i] << endl;
                return 0;
            }
        }
        cout << LagrangeInterpolation(N) << endl;
    }

    return 0;
}