#include<bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;

#define rep(i, a, b) for(ll i = (ll)a; i < (ll)b; i++)
#define irep(i, v) for(auto i = (v).begin(); i != (v).end(); i++)
#define ALL(v) (v).begin(), (v).end()
#define SZ(v) (ll)(v).size()

const ll INF = 1e18;
const ld EPS = 1e-10;

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  srand((unsigned)time(NULL));
  cout << fixed << setprecision(20);


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


  return 0;
}