import java.util.*;

public class Exercise121{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    long l = sc.nextInt();

    long a = (l - 1) / 2;
    long b = (l - 3) / 2;
    System.out.println(a * (a + 1) / 2 + b * (b + 1) / 2);
	}
}