#include <bits/stdc++.h>
using namespace std;

int main() {
  int N, K, memo, answer;
  cin >> N >> K;
  answer = 0;
    for (int i = K; i <= N + 1; i++) {
    memo = N*i - i*i + i + 1;
    answer += memo % 1000000007;
    }
  cout << answer << endl;
}
