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 K = sc.nextInt();

		int ans = 0;

		if(K%2==0) {

			ans = (K/2)*(K/2);

		}else {

			ans = (K/2)*((K/2)+1);

		}

		System.out.println(ans);

	}

}
