import java.util.*;

public class Exercise123{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int d = sc.nextInt() / 2;
    int max = 0;
    for(int i = 0; i < d; i++){
      int s = i * (d - i);
      max = Math.max(max, s);
    }
    System.out.println(max);
	}
}