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 Java (OpenJDK 1.8.0) (judge verdict: Accepted)

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            long N = in.nextInt();
            long K = in.nextInt();

            long count = 0;
            for (long a = 1; a <= N; a++) {
                {
                    long b = (K * a - a) % K;
                    if (b == 0) {
                        b = K;
                    }
                    long c = (K * b - b) % K;
                    if (c == 0) {
                        c = K;
                    }
                    if ((c + a) % K != 0) {
                        continue;
                    }
                    count += ((N - b) / K + 1) * ((N - c) / K + 1);
                }
            }

            System.out.println(count);
        }
    }
}