#include <bits/stdc++.h>
using namespace std;

int main(){
  int n;
  cin >> n;
  int ans =0;
  vector <int> a (n);
  for(int i =0; i<n;i++ ){
    a.at(i) = i+1;
    ans+=a.at(i);

  }
  cout << ans << endl;
}