#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const double PI = acos(-1);
const ll MOD = 1000000007;

int f(int x) {
  if (x == 0) return 0;
  return x + f(x-1);
}

int main() {
  int N; cin >> N;
  cout << f(N) << endl;  
}