#include <vector>
#include <queue>
#include <deque>
#include <stack>
#include <algorithm>
#include <functional>
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <ctime>
#include <cctype>
#include <string>

using namespace std;

typedef long long ll;

int main() {
  ll l;
  cin >> l;
  cout << (l-1)*(l-1)/4 << endl;
}