#include <iostream>
#include <vector>
#include <utility>
#include <algorithm>
#include <string>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using vll = vector<long long>;
using vpll = vector<pair<ll, ll>>;
using vull = vector <unsigned long long>;

void solve() {
  ll n;
  cin >> n;
  cout << n * (n + 1) / 2;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  ll t = 1;
  
  //cin >> t;
  
  while (t--) {
    solve();
  }  
}