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 Rust (1.15.1) (judge verdict: Accepted)

fn read_usizepair() -> (usize, usize) {
    let mut input = String::new();
    let _ = std::io::stdin().read_line(&mut input);
    let v: Vec<usize> = input
        .trim()
        .split_whitespace()
        .map(|x| x.parse().unwrap())
        .collect();
    (v[0], v[1])
}

fn main() {
    let (n, k) = read_usizepair();

    if k % 2 != 0 {
        println!("{}", ((n / k) as i64).pow(3))
    } else {
        println!("{}", ((n / k) as i64).pow(3) + (((n + k / 2) / k) as i64).pow(3));
    }
}