#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
long long primeNumber(long long x) {
  bool fire = true;
  for(int i = 2; i <= sqrt(x); i++) {
    if(x % i == 0) {
      fire = false;
    }
  }
  return fire;
}
int main() {
  long long N; cin >> N;
  long long X = (N + 1) / 2;
  cout << (X + 1ll) * X / 2 << endl;
}