#include <bits/stdc++.h>
using namespace std;
using ll = long long;

istream &operator>>(istream &is, __int128_t &v) {
  string s;
  is >> s;
  v = 0;
  for(const auto &i : s) {
    if(isdigit(i)) { v = v * 10 + i - '0'; }
  }
  if(s[0] == '-') { v = -v; }
  return is;
}

ostream &operator<<(ostream &os, const __int128_t &v) {
  if(!v) { return (os << "0"); }
  __int128_t n = v;
  if(v < 0) {
    os << '-';
    n = -n;
  }
  string s;
  for(; n; n /= 10) { s += (n % 10) + '0'; }
  ranges::reverse(s);
  return (os << s);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);

  __int128_t N;
  cin >> N;

  cout << N * (N + 1) / 2 << "\n";
}