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