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