// #define DEBUG_ON

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define timer_start()                          \
  chrono::system_clock::time_point start, end; \
  start = chrono::system_clock::now();
#define timer_wrap()                                                     \
  end = chrono::system_clock::now();                                     \
  double time = static_cast<double>(                                     \
      chrono::duration_cast<chrono::microseconds>(end - start).count() / \
      1000.0);                                                           \
  printf("time %lf[ms]\n", time);                                        \
  start = end;
#define optimize_cin() \
  cin.tie(0);          \
  ios::sync_with_stdio(false)
using namespace std;
using ll = long long;
#define INF 1000000000  // 10^9
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}
int main() {
  // input
  int t;
  cin >> t;
#ifdef DEBUG_ON
  timer_start();
#endif
  int sum;
  for (int i = 1; i <= t; i++) {
    sum += i;
  }

  cout << sum << endl;

#ifdef DEBUG_ON
  timer_wrap();
#endif
  return 0;
}