#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, k;
  cin >> n >> k;
  vector<int> p(n + 1);
  for (int i = 0; i <= n; i++) p[i] = i;
  vector<long> q(n + 2);
  q[0] = 0;
  for (int i = 1; i <= n + 1; i++) q[i] = q[i - 1] + p[i - 1];
  long ans = 0;
  long mod = 1000000007;
  for (int i = k; i <= n + 1; i++) {
    ans += (q[n + 1] - q[n + 1 - i] - q[i] + 1) % mod;
  }
  cout << ans % mod << endl;
}
