Problem:
Score : 300 points

Problem Statement

You are given integers N and K. Find the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.
The order of a,b,c does matter, and some of them can be the same.

Constraints

1 \leq N,K \leq 2\times 10^5

N and K are integers.

Input

Input is given from Standard Input in the following format:

N K

Output

Print the number of triples (a,b,c) of positive integers not greater than N such that a+b,b+c and c+a are all multiples of K.

Sample Input 1

3 2

Sample Output 1

9

(1,1,1),(1,1,3),(1,3,1),(1,3,3),(2,2,2),(3,1,1),(3,1,3),(3,3,1) and (3,3,3) satisfy the condition.

Sample Input 2

5 3

Sample Output 2

1

Sample Input 3

31415 9265

Sample Output 3

27

Sample Input 4

35897 932

Sample Output 4

114191

Solution in Java8 (OpenJDK 1.8.0) (judge verdict: Wrong Answer)

import java.math.BigInteger;
import java.util.Scanner;

public class Main implements Runnable {

    private static Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        new Thread(null, new Main(), "", 128 * 1024 * 1024).start();
    }

    public void run() {
        long n = sc.nextLong(), k = sc.nextLong();
        boolean div = k % 2 == 0;
        long divk = 1;
        if (k / 2 + k > n) {
            divk = 0;
        }

        if (div && k > n && k <= n * 2) {
            System.out.println(1);
        } else {
            BigInteger nk = BigInteger.valueOf(n / k);
            nk = nk.pow(3);
            if (div) {
                BigInteger nkd = BigInteger.valueOf(n / k + divk);
                nk = nk.add(nkd.pow(3));
            }
            System.out.println(nk);
        }
    }
}