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: Runtime Error)

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner stdin = new Scanner(System.in);
		int n, k;
		n = stdin.nextInt();
		k = stdin.nextInt();

		int count = 0;
		for (int i = 1; i <= n; i++)
			for (int j = i; j <= n; j++)
				if ((i + j) % k == 0)
					for (int kk = j; kk <= n; kk++)
						if ((j + kk) % k == 0)
							if ((i + kk) % k == 0)
								if (i == j && j == kk && kk == i)
									count++;
								else
									count += 3;

		System.out.println(count);
		stdin.close();
	}
	/*
	 * 111 112 113 121x 122 123 131x 132x 133 6way
	 * 
	 * 211x 212x 213x 221x 222 223 231x 232x 233 3way
	 * 
	 * 311x 312x 313x 321x 322x 323x 331x 332x 333 1way
	 */

}