#include <bits/stdc++.h>
using namespace std;
using ll = long long;
ll mod = 1e9+7;

ll nPk(ll n, ll k){
    ll ans = 1;
    for (ll i = 0; i < k; ++i){
        ans = (ans * (n - i)) % mod;
    }
    return ans;
}

ll solve(ll N, ll K){
    ll ans, tmp1, tmp2;
    if (N == 1) return 0;
    if (K == 1){
        ans = (nPk(N, K) + mod - 1) % mod;
        tmp1 = (N * (N + 1) / 2) % mod;
        return (ans * tmp1) % mod;
    }
    ans  = nPk(N - 2LL, K - 2LL);
    tmp1 = (N - K) * (N - 1LL) % mod;
    tmp1 *= ((N + 1LL) * N / 2) % mod;
    tmp1 %= mod;
    tmp2 = (K * (K - 1) / 2) % mod;
    tmp2 *= ((N - 1) * N / 2) % mod;
    tmp2 %= mod;
    ans *= (tmp1 + tmp2) % mod;
    ans %= mod;
    return ans;
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll N, K;
    cin >> N >> K;
    cout << solve(N, K) << endl;
    return 0;
}