#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int t;
  t = 1;
  while (t--) {
    int n;
    cin >> n;
    cout << (n + 1) * (n + 1) / 4 << endl;
  }
  return 0;
}
