#include <bits/stdc++.h>

using namespace std;
typedef long long ll;

int main() {
  ll L;
  scanf("%lld", &L);
  ll n_a = ceil((double)L / 2);
  ll n_b = L - n_a;
  ll ans = (n_a * (n_a - 1) / 2) + (n_b * (n_b - 1) / 2);
  printf("%lld\n", ans);
  return 0;
}