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 sc = new Scanner(System.in);
		
		int K = sc.nextInt();
		int ANS = 0;
		int K2 = K / 2;
		if (K % 2 == 0){
			ANS = K2 * K2;
		}else{
			K2 = K2 + 1;
			ANS = K2 * K2;
			ANS = ANS - K2;
		}
		System.out.println(ANS);
		
	}
}
