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 (1.42.0) (judge verdict: Accepted)

use std::io;
use std::str::FromStr;

fn input_tuple() -> (u128, u128) {
    let mut line: String = String::new();
    io::stdin().read_line(&mut line);
    let vec: Vec<u128> = line.split_whitespace().map(|s| s.parse().unwrap()).collect();
    (vec[0], vec[1])
}

fn main() {
    let (n, k) = input_tuple();
    let mut half_count = 0u128;
    let mut zero_count = 0u128;
    for i in 1..(n+1) {
        if i % k == 0 {
            zero_count += 1;
        }
        if k % 2 == 0 && (i % k) == (k / 2) {
            half_count += 1;
        }
    }
    // println!("{} {}", zero_count, half_count);
    println!("{}", zero_count * zero_count * zero_count + half_count * half_count * half_count);
}