#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
using namespace std;

int noa(int n) {
  int res = 1;
  for (int i = 1; i <= n; i++) {
    res += i;
  }
  return res;
}

int main(int argc, char **argv)
{
  int n;
  while (cin >> n) {
    if (!n)
      break;
    cout << noa(n) << endl;
  }
  return 0;
}