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.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ABC108C_cs
{
    class Program
    {
        static void Main(string[] args)
        {
            var nk = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            var n = nk[0];
            var k = nk[1];
            if (k % 2 == 1)
            {
                int x = n / k;
                Console.WriteLine((long)x * x * x);
            }
            else
            {
                int counta = 0;
                int countb = 0;
                for (int i = 1; i <= n; i++)
                {
                    if (i % k == 0)
                    {
                        counta++;
                    }
                    if (i % k == k / 2)
                    {
                        countb++;
                    }


                }
                Console.WriteLine((long)counta * counta * counta + countb * countb * countb);
            }

        }
    }
}