#include <bits/stdc++.h>

using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;

#define repi(i,a,b) for(ll i=a;i<b;i++)
#define rep(i,a) repi(i,0,a)
#define rrep(i,a) for(ll i=a-1;i>=0;i--)
#define MOD 1000000007

//debug
#define debug(arr) cerr<<#arr<<"(l"<<__LINE__<<") : ";for(auto x:arr)cerr<<x<<" ";cerr<<endl;

ll modinv(ll a, ll m) {
    ll b = m, u = 1, v = 0;
    while (b) {
        ll t = a / b;
        a -= t * b; swap(a, b);
        u -= t * v; swap(u, v);
    }
    u %= m;
    if (u < 0) u += m;
    return u;
}

int main(){
  ll N, K;
  cin >> N >> K;

  ll ans = (N-K)*(N+1) + K*(K-1)/2;
  repi(i, N-K+1, N+1) ans = ans * i % MOD;
  ans = ans * modinv(2, MOD) % MOD;
  cout << ans << endl;

  return 0;
}