#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false); cin.tie(0);
  long long n, k;
  cin >> n >> k;
  cout << k * (n + n - k + 1) / 2 + 1 << endl;
  return 0; 
}