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.*;

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