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 Scala (2.11.7) (judge verdict: Wrong Answer)

import scala.io.StdIn._
object Main extends App {
  val Array(n, k) = readLine.split(" ").map{_.toInt}
  println(if ((k & 1) == 1) calcOdd(n, k) else calcEven(n, k))

  def calcOdd(n: Int, k: Int): Long = {
    val l = n.toLong / k
    l * l * l
  }

  def calcEven(n: Int, k: Int): Long = {
    ((k / 2) to k by (k / 2)).map {a =>
      val l = (n - a).toLong / k + (if ((n - a) % k == 0) 0 else 1)
      l * l * l
    }.sum
  }
}