#include <iostream>
#define llint long long

using namespace std;

llint n, k;

int main(void)
{
  cin >> n >> k;
  llint x = k*n - k*(k-1)/2 + 1, m = n*(n+1)/2 + 1;
  if(x >= m){
    cout << m << endl;
  }else{
    cout << x << endl;
  }
  return 0;
}