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)

// デバッグ実行：Ctrl+F5

using System;

class Program
{
    static void Main(string[] args)
    {
        String line;
        line = Console.ReadLine();
        String[] words = line.Split(' ');

        int N = int.Parse(words[0]);
        int K = int.Parse(words[1]);
        int count = 0;
        int plus = N / K;
        count = plus * plus * plus;
        // 次に、Kの倍数でないもの
        for (int i = 1; i <= N; i++)
        {
            if (i % K == 0)
            {
                continue;
            }
            if ((i % K + i % K) % K == 0)
            {
                plus = N + (i % K);
                plus /= K;
                count += plus * plus;
            }
        }
        Console.WriteLine(count);
    }
    
}