#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(int i = m;i >= n;--i)
#define INF INT_MAX/2
using namespace std;
using ll = long long;
using R = double;
using Data = pair<ll, vector<int>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 50;
struct edge { ll from; ll to; ll cost; };

ll modp(ll n,ll k) {
	ll ret = 1;
	for (ll i = n; i >= n - k + 1; i--) {
		ret *= i;
		ret %= MOD;
	}
	return ret%MOD;
}

int main() {
	ll n, k;
	cin >> n >> k;

	ll ans = 0;
	ll num1 = modp(n - 1, k);
	ll num2 = modp(n - 2, k - 2)*k*(k - 1) / 2;
	num2 %= MOD;
	for (ll i = 1; i <= n; i++) {
		if (i == n) {
			ans += i * num1;
		}
		else {
			ans += i * (num1 + num2);
		}
		ans %= MOD;
	}
	cout << ans%MOD<< endl;

	return 0;
}