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;

namespace Atcoder
{
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] input = Console.ReadLine().Split(' ');
            int n = int.Parse(input[0]);
            int k = int.Parse(input[1]);

                if (k % 2 != 0)
                {
                    int x = k;
                    int b = 0;
                    while (x <= n)
                    {
                        b++;
                        x += k;
                    }
                    Console.WriteLine(b * b * b);
                }
                else
                {
                    int x = k / 2;
                    int b = 0;
                    int sp = 0;
                    bool isbaisuu = false;
                    while (x <= n)
                    {
                        if (isbaisuu)
                        {
                            b++;
                            isbaisuu = false;
                        }
                        else
                        {
                            sp++;
                            isbaisuu = true;
                        }
                    x += (k / 2);
                    }
                    Console.WriteLine(b * b * b + sp * sp * sp);
                }
            }
        }

}