#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int main(void) {
  ll L;
  cin >> L;

  ll A = (L - 1) / 2, B = (L - 3) / 2;
  cout << A * (A + 1) / 2 + B * (B + 1) / 2 << endl;

  return 0;
}