#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void printL(auto a){
  cout << a << endl;
}

void L(){
  cout << endl;
}

int main(){
  int N; cin >> N;
  ll ans = 0;
  for(int i = 1; i <= N; i++){
    ans += i;
  }
  printL(ans);
}