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: Accepted)

using System;
using System.IO;
using System.Linq;

namespace Triangular_Relationship
{
    class Program
    {
        public static void Main(string[] args)
        {
            using (var sc = new SetConsole())
            {
                var input = GetArrayIntInput();
                var n = input[0];
                var k = input[1];
                var count = (long)Math.Pow(n / k, 3);
                if (k % 2 == 0)
                {
                    count += (long)Math.Pow((n + (k / 2)) / k, 3);
                }
                CWrite(count);
            }
        }

        static string[] GetArrayCharInput() => Console.ReadLine().Split();
        static int[] GetArrayIntInput() => Console.ReadLine().StringToIntArray();
        static int GetIntInput() => Console.ReadLine().ToInt();
        static void CWrite<T>(T str) => Console.WriteLine(str);

    }

    class SetConsole : IDisposable
    {
        StreamWriter sw = new StreamWriter(Console.OpenStandardOutput());
        public SetConsole()
        {
            sw.AutoFlush = false;
            Console.SetOut(sw);
        }
        public void Dispose()
        {
            Console.Out.Flush();
            sw.AutoFlush = true;
            Console.SetOut(sw);
        }
    }

    static class ExtentionsLibrary
    {
        public static int[] StringToIntArray(this string str) =>
            str.Split().Select(int.Parse).ToArray();
        public static int ToInt(this string str) => int.Parse(str);
    }
}