import java.util.*;
import java.math.*;

public class Main {
    private static Scanner sc = new Scanner(System.in);
    public static void main(String[] args) throws Exception {
        int l = (sc.nextInt()-1)/2;
        BigDecimal a = new BigDecimal(l);
        BigDecimal b = new BigDecimal(l);
        System.out.println(a.multiply(b));
    }
}