#include <bits/stdc++.h>
#define rep(i, ns, ne) for (int i = ns; i < ne; ++i)
using namespace std;

int main() {
  int n, ans = 0;
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    ans += i;
  }
  cout << ans << endl;
  getchar();
}