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: Time Limit Exceeded)

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

namespace ABC
{
    class Program
    {
        static void Main(string[] args)
        {
            var split = Console.ReadLine().Split(' ');
            int N = int.Parse(split[0]);
            int K = int.Parse(split[1]);
            //準備完了
            long output = 0;
            for (int a_i = 1; a_i <= N; a_i++)
            {
                //bの初期値は(a_i/K)にK+1をかけて、a_iを引いたもの、そこに
                for (int b_i = ((a_i / K) * (K) + K - a_i); b_i <= N; b_i += K)
                {
                    for (int c_i = ((a_i / K) * (K)+K - a_i); c_i <= N; c_i += K)
                    {
                        if ((b_i + c_i) % K == 0)
                        {
                            output++;
                            
                        }
                    }


                } 
            }
            Console.WriteLine(output);
        }

    }
}