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


}
}