#include"bits/stdc++.h"

using namespace std;
using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#define FOR(k,m,n) for(ll (k)=(m);(k)<(n);(k)++)
#define REP(i,n) FOR((i),0,(n))
#define WAITING(str) int str;std::cin>>str;
#define DEBUGING(str) cout<< #str << " " str<<endl

constexpr int INF = (1 << 30);
constexpr ll INFL = (1ll << 60);
constexpr ll MOD = 1000000007;// 10^9+7

ll P(ll l, ll r) {
	ll res = 1;
	REP(i, r)res = (res*(l - i)) % MOD;
	return res;
}

int main()
{
	ll N, K;
	cin >> N >> K;
	ll left = (N - 1)*N / 2 % MOD;
	ll way = (P(N - 1, K) + (P(N, K) - P(N - 1, K) * 2 + P(N - 2, K)) / 2) % MOD;
	ll right = P(N, K + 1);
	cout << (left*way + right) % MOD << endl;
	return 0;
}