Find the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive). The order does not matter.

Constraints

* 2\leq K\leq 100
* K is an integer.

Input

Input is given from Standard Input in the following format:


K


Output

Print the number of ways to choose a pair of an even number and an odd number from the positive integers between 1 and K (inclusive).

Examples

Input

3


Output

2


Input

6


Output

9


Input

11


Output

30


Input

50


Output

625
import java.util.*; 
public class Main {

  public static void main(String[] args) {
  
  Scanner sc=new Scanner(System.in);
  int a[]=new int[3];
  a[0]=sc.nextInt();
  int b=a[0]/2;



  System.out.println(b*(a[0]-b));
  }
  
}