Problem:
Score : 100 points

Problem Statement

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).

Sample Input 1

3

Sample Output 1

2

Two pairs can be chosen: (2,1) and (2,3).

Sample Input 2

6

Sample Output 2

9

Sample Input 3

11

Sample Output 3

30

Sample Input 4

50

Sample Output 4

625

Solution in Java (OpenJDK 11.0.6) (judge verdict: Runtime Error)

package abc108;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
//偶数と奇数の組み合わせ(%2,%2+1)

		Scanner scanner=new Scanner(System.in);
		int K=scanner.nextInt();
		int kosuu=((K/2)*((K+1)/2));

		System.out.println(kosuu);
	}

}