#include <bits/stdc++.h>
using namespace std;
int main() {
  int a;
  cin >> a;
  if (a % 2 == 0) {
    cout << (a / 2) * ((a / 2) + 1) << endl;
  } else {
    cout << (a / 2) * ((a / 2) + 1) + (a / 2) + 1 << endl;
  }
  return 0;
}
