#include <bits/stdc++.h>
#include <iostream>
#include <string>
#include <vector>

using namespace std;
#define rep(i,n) for(int i=0;i<n;i++)
typedef long long ll;

int main(){
  int n;
  cin >> n;
  int sum = 0;
  rep(i,n){
    sum += n-i;
  }
  cout << sum << endl;
}