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 in = new Scanner(System.in);
	int a = in.nextInt();
	int sol = 0;
	for (int i = 1; i <= a; i++) {
	    for (int j = 1; j<= a; j++) {
		if (i%2 == 0 && j%2 != 0)
		    sol++;
	    }
	}
	System.out.println(sol);
    }
}
