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: Time Limit Exceeded)

using System;
using System.Collections.Generic;

namespace AtCoder
{
	public class Program
	{
		// ABC108-C
		static void Main(string[] args)
		{
			string[] sv = Console.ReadLine().Split();
			int N = int.Parse(sv[0]);
			int K = int.Parse(sv[1]);
			int count = 0;
			for (int x = K; x <= 2 * N; x += K) {
				//System.Diagnostics.Debug.WriteLine(string.Format("{0} <= {1} = 2 * {2}", x, 2 * N, N));
				for (int a = 1; a <= N; a++) {
					int b = x - a;
					if (0 < b && b <= N) {
						if (a - b == 0 || (a - b) % K == 0) {
							for (int c = K - Math.Min(a, b); c <= N; c += K) {
								if (c > 0) {
									count++;
									//System.Diagnostics.Debug.Write(string.Format("a({0},{1},{2}) ", a, b, c));
								}
							}
						}
					}
				}
				//System.Diagnostics.Debug.WriteLine("");
			}
			Console.WriteLine(count);
		}
	}
}