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;

namespace Practice
{
    class Program
    {
        private static int ReadAndParseInt()
        {
            return int.Parse(Console.ReadLine());
        }
        private static int[] ReadAndParseIntArr()
        {
            return Array.ConvertAll(Console.ReadLine().Split(' '), int.Parse);
        }
        private static long ReadAndParseLong()
        {
            return long.Parse(Console.ReadLine());
        }
        private static long[] ReadAndParseLongArr()
        {
            return Array.ConvertAll(Console.ReadLine().Split(' '), long.Parse);
        }
        static void Main(string[] args)
        {
            SolveA(args);
            //SolveB(args);
            //SolveC(args);
            //SolveD(args);


        }

        static void SolveA(string[] args)
        {
            int[] nk = ReadAndParseIntArr();
            int n = nk[0];
            int k = nk[1];
            int cnt = 0;
            if( k % 2 == 0)
            {
                int tmp = k / 2;
                int cntA = 0;
                int cntB = 0;
                for(int i=1;i<=n;++i)
                {
                    if( i % k == 0 )
                    {
                        cntA++;
                    }
                    if( i%k == tmp)
                    { cntB++; }
                }
                cnt = cntA * cntA * cntA + cntB * cntB * cntB;
            }
            else
            {
                for(int i=1;i<=n;++i)
                {
                    if( i % k == 0)
                    {
                        cnt ++;
                    }
                }
                // cntの数の組み合わせ
                cnt = cnt * cnt * cnt;
            }

            Console.WriteLine(cnt);
        }
    }
}