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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;


public class MyProgram
{	
  
    public static void Main()
	{
        int[] n = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
        int N = n[0];
        int K = n[1];
        long c1 = 0, c2 = 0;
        for(int i = 1 ; i <= N ; i++)
        {
            if(K%2 == 0 && i%K == K/2)
            {
                c2++;
            }
            else if(i%K == 0)
            {
                c1++;

            }
        }
        Console.WriteLine(Math.Pow(c1,3)+Math.Pow(c2,3));
    }
}