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;

public class AtCoder{
	public static void Main(){
		string[] s;
		s = Console.ReadLine().Trim().Split(' ');
		
		int n, k;
		n = int.Parse(s[0]);
        k = int.Parse(s[1]);
		
	    int x = n/k;
	    int y;
	    double z;
		
		if (k%2 == 1){
			z = Math.Pow(x,3);
		} else {
		    k = k / 2;
		    y = (n-k)/(2*k) + 1;
			z = Math.Pow(x,3) + Math.Pow(y,3);
		}
		Console.WriteLine(z);
	}
}