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: Accepted)

import java.util.*;

public class Main {
  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int N = sc.nextInt();
    int K = sc.nextInt();
    ArrayList<Integer> even = new ArrayList<>();
    ArrayList<Integer> odd = new ArrayList<>();
    if (K % 2 == 1) { // Kが奇数
      for (int i = 1; i <= N; i++) {
        if (i % K == 0) {
          odd.add(i);
        }
      }
    } else { // Kが偶数
      for (int i = 1; i <= N; i++) {
        if (i % K == 0) {
          odd.add(i);
        } else if (i % K == K / 2) {
          even.add(i);
        }
      }
    }
    System.out.println((long) Math.pow((double) odd.size(), 3.0) + (long) Math.pow((double) even.size(), 3.0));
  }
}