#include <bits/stdc++.h>
using namespace std;
#ifdef LOCAL
  #include "settings/debug.cpp"
#else
  #define Debug(...) void(0)
#endif
#define rep(i, n) for (int i = 0; i < (n); ++i)
using ll = long long;
using ull = unsigned long long;

int main() {
  ull n;
  cin >> n;
  if (n % 2 == 0) {
    cout << n / 2 * (n + 1) << endl;
  }
  else {
    cout << (n + 1) / 2 * n << endl;
  }
  return 0;
}