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.Collections.Generic;

namespace AtCoder
{
	public class Program
	{
		// ABC108-C ng
		static void Main(string[] args)
		{
			string[] sv = Console.ReadLine().Split();
			int N = int.Parse(sv[0]);
			int K = int.Parse(sv[1]);
			long c1 = 0, c2 = 0;
			for (int i = 1; i <= N; i++) {
				if (i % K == 0) {
					c1++;
					//System.Diagnostics.Debug.WriteLine(i);
				} else if (K % 2 == 0 && i % K == K / 2) {
					c2++;
					//System.Diagnostics.Debug.WriteLine(i);
				}
			}
			Console.WriteLine(c1 * c1 * c1 + c2 * c2 * c2);
		}
	}
}