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 n = sc.nextInt();
		int ki = 0,gu = 0;
		for (int i = 0; i < n; i++) {
			if(i % 2 == 0) {
				gu++;
			}else {
				ki++;
			}
		}
		System.out.println(gu*ki);
	}

}
