#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
  ll l;
  cin >> l;
  ll a = (l + 1) / 2;
  ll b = l - a;
  cout << a * (a - 1) / 2 + b * (b - 1) / 2 << endl;
  return 0;
}