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 scan = new Scanner(System.in);
		
		int num = scan.nextInt();
		
		scan.close();

		int A = num / 2;
		int B = num % 2 == 1 ? A + 1 : A;
		
		System.out.print(A * B);
	}
}
