/**
 *   @FileName	a.cpp
 *   @Author	kanpurin
 *   @Created	2020.06.13 16:39:42
**/

#include "bits/stdc++.h" 
using namespace std; 
typedef long long ll;

int main() {
    ll n,k;cin >> n >> k;
    cout << k * (2 * n - k + 1) / 2 + 1 << endl;
    return 0;
}