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.Linq;
using System.Collections.Generic;

class Cmondai
{
    static void Main()
    {
        var nk = Console.ReadLine().Split(' ').Select(x => Int64.Parse(x)).ToArray();
        var N = nk[0];
        var K = nk[1];
        var ans = 0L;
        var count = 0L;
        var num = K;
        var index = 2L;
        //余り0
        while (num<=N)
        {
            count++;
            num = K*index;
            index++;
        }
        ans += (int)Math.Pow(count,3);
        //余り1/2
        if (K % 2 == 0)
        {
            var add = K / 2;
            count = 1;
            num = 1;
            index = 1;
            while (num <= N)
            {
                num = K * index;
                if (num+add<=N)count++;
                index++;
            }
            ans += (int)Math.Pow(count,3);
        }
        Console.WriteLine(ans);
    }
}