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 Java8 (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main{
	public static void main(String[] args) {
		Scanner scan = new Scanner(System.in);
		int input = scan.nextInt();
		scan.close();
		int even = 0;
		int odd = 0;

		if(input % 2 == 1) {
          int a = input;
			while (a != 1) {
				a = a - 2;
				odd++;
			}
			even = input - odd;
		}else {
          int a = input;
			while (a != 0) {
				a = a - 2;
				even++;
			}
			odd = input - even;
		}
		System.out.println(odd * even);
	}
}