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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php

fscanf(STDIN, "%d %d", $n, $k);

if ($k % 2 === 1) {
    $x = floor($n / $k);

    // NOTE: intにキャストしないとなぜか指数表現になる
    echo (int) pow($x, 3);
} else {
    $count1 = 0;
    $count2 = 0;
    for ($i = 1; $i <= $n; ++$i) {
        $mod = $i % $k;
        if ($mod === 0) {
            ++$count1;
        } elseif ($mod === ($k / 2)) {
            ++$count2;
        }
    }

    echo (int) pow($count1, 3) + (int) pow($count2, 3);
}