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 n = sc.nextInt();
        
        int g = n / 2;
        int k = n % 2 == 0 ? (n / 2) : (n / 2 + 1);
        System.out.println(g * k);
    }
}