#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vector<int>>;
using vvl = vector<vector<ll>>;

// 0 -> 0
// 1 -> n
// 2 -> n + n - 1

// k -> n + .. + n - k
//    = n * k - k * (k - 1) / 2

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  ll n, k;
  cin >> n >> k;
  cout << 1 + n * k - k * (k - 1) / 2 << endl;
  return 0;
}