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 OCaml (4.10.0) (judge verdict: Wrong Answer)

let n, k = Scanf.sscanf (read_line ()) "%d %d" @@ fun n k -> (n, k)

let rec pow x n = if n = 1 then x else x * pow x (n - 1)

let () =
  let a = n / k in
  let b = (n - k / 2) / k + 1 in
  Printf.printf "%d\n" @@ pow a 3 + if k mod 2 = 0 then pow b 3 else 0