#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<vector>
#include<map>
#include<queue>
#include<string>
#include<sstream>
#include<cmath>
#include<numeric>
using namespace std;


int main(){

  int n;
  cin >> n;
  cout << n * (n+1) / 2 << endl;

  return 0;
}