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 gn=0;
		int kn=0;

		for(int i=1;i<=k;i++){
			if(i%2==0){
				gn++;
			}else{
				kn++;
			}
		}
		System.out.println(gn*kn);

	}



}
