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;


public class C{
	
	public static void Main(){
	
		string[] args = Console.ReadLine().Split(' ');
		long n = Int64.Parse( args[0] );
		long k = Int64.Parse( args[1] );
		
		long num = n / k;
		long result = num * num * num;
		if( k % 2L == 0L ){
			num = 0L;
			for( long i = 1L; i <= n; i++ ){
				if( i % k == k/2L ) num++;
			}
			result += num * num * num;
		}
		Console.WriteLine(result);

	}

}