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;

class Main {
	public static void main(String[] args) {
		Scanner stdIn = new Scanner(System.in);
		
		int k = stdIn.nextInt();
		
		if (k % 2 == 0) {
			System.out.println(k*k/4);
			return;
		}
		if (k % 2 == 1) {
			System.out.println((k-1)*(k-1)/4 + k/2);
			return;
		}
		
	
	}

}