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 ABC108C
{
    static class MainClass
    {
        public static void Main(string[] args)
        {

            string[] input1 = Console.ReadLine().Split(' ');
            int N = int.Parse(input1[0]);
            int K = int.Parse(input1[1]);

            long cnt = 0;
            long ans = 0;
            long cntk2 = 0;
            long cntk0 = 0;
            if (K % 2 == 1)
            {
                cnt = N / K;

                ans = cnt * cnt * cnt;

            }
            else
            {
                //あまりがK/2のもののペア
                cntk2 = (int)Math.Pow((N + (K / 2)) / K,3);

                //あまりが0のもののペア
                cntk0 = (int)Math.Pow(N / K, 3);

                ans = cntk2 + cntk0;
            }

            Console.WriteLine(ans);
            return;

        }


        public static int Gcd(int a, int b){
            int tmp;
            // a<bにする
            if(a >=b){
                tmp = a;
                a = b;
                b = tmp;
            }

            if (a == 0){
                return b;
            }

            tmp = a;
            a = b % a;
            b = tmp;
            return Gcd(a, b);

        }


    }

}