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;

namespace AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var dg = Console.ReadLine().Split(' ').Select(v => int.Parse(v)).ToArray();

            var n = dg[0];
            var k = dg[1];

            var res = 0;
            if (k % 2 == 0)
            {
                var a = 0;
                var b = 0;
                int div = k / 2;
                for (int i = 1; i <= n; ++i)
                {
                    if (i % k == 0)
                    {
                        ++a;
                    } else if (i % k == div)
                    {
                        ++b;
                    }
                }

                res = (int)(Math.Pow(a, 3) + Math.Pow(b, 3));
            } else
            {
                for (int i = 1; i <= n; ++i)
                {
                    if (i % k == 0)
                    {
                        ++res;
                    }
                }

                res = (int)Math.Pow(res, 3);
            }
            
            Console.WriteLine(res);
        }
    }
}