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 static System.Console;

class Program
{

    static void Main(string[] args)
    {
        var input = Array.ConvertAll(ReadLine().Split(),int.Parse);
        var n = input[0];
        var k = input[1];
        var count = 0;
        
        if (k % 2 == 0)//kが偶数
        {
            //余りがk/2
            for (var i = 1; i <= n; i++)
            {
                if (i % k == k / 2) count++;
            }
            count = count * count * count;

            //余りがゼロ
            var temp = n / k;
            count += temp * temp * temp;
        }
        else//kが奇数
        {
            //余りがゼロ
            var temp = n / k;
            count += temp * temp * temp;
        }

        WriteLine(count);
    }
}