import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    long L = sc.nextLong();
    long a = (L + 1) / 2;
    long b = (L - 1) / 2;
    long ans = (a * (a - 1)) / 2 + (b * (b - 1)) / 2;
    System.out.println(ans);
  }
}