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.Scanner;

public class Main {

	public static void main(String args[]) {
		    Scanner sc = new Scanner(System.in);

		    int a = sc.nextInt();
		    if(a % 2 == 0) {
		    	System.out.println(a * a / 4);
		    }
		    else {
		    	System.out.println((a+1)/2*(a/2));
		    }
		    sc.close(); }
}