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.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

  public static void main(String[] args) {
    
    new Main().run();
  }

  public void run(){

    try(BufferedReader in = new BufferedReader(new InputStreamReader(System.in))) {

      String[] lines = in.readLine().split(" ");
      int n = Integer.parseInt(lines[0]);
      int k = Integer.parseInt(lines[1]);

      long ans;
      if((k & 1) == 0) {
        long a = n / k;
        long b = n / (k / 2);
        long c = b - a;
        ans = (a * a * a) + (c * c * c);
      } else {
        long a = n / k;
        ans = a * a * a;
      }

      System.out.println(ans);
    }
    catch(IOException e) {
      System.err.println(e);
    }
  }
}