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;

namespace ABC108_C{
    class Program{
        static void Main(string[] args){
            var input  = Console.ReadLine().Split(' ');
            var n = long.Parse(input[0]);
            var k = long.Parse(input[1]);

            var ans = (long)Math.Pow(n / k,3);
            var temp = 0;
            if(k % 2 == 0){
                for(var i = 1;i <= n;i++){
                    if(i % k == k / 2){
                        temp++;
                    }
                }
            }
            ans += (long)Math.Pow(temp,3);
            Console.WriteLine(ans);
        }
    }
}