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.*;

public class Main{
	public static void main(String[] args){
		Scanner scanner = new Scanner(System.in);
		int k = scanner.nextInt();
                int kk = k/2;
		if(k%2==0){
			System.out.print(kk * kk);
			System.exit(0);
		}
		System.out.print(kk + kk * kk);
	}
}