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)

#![allow(non_snake_case)]
#![allow(unused_imports)]
use proconio::input;
use std::cmp::max;
use std::cmp::min;
use std::collections::HashMap;
use std::collections::VecDeque;

fn main() {
    input! {
        N: usize,
        K: usize,
    }

    // 2(a + b + c) % K == 0

    if K % 2 == 0 {
        // a + b + c % (K/2) == 0
        // a, b, cはそれぞれ (K/2)の倍数

        // ききき、ぐぐぐ
        let k = K / 2;
        dbg!(k);
        let c: usize = N / k;
        dbg!(c);
        let ans = if c % 2 == 0 {
            (c / 2) * (c / 2) * (c / 2) + (c / 2) * (c / 2) * (c / 2)
        } else {
            ((c - 1) / 2 + 1) * ((c - 1) / 2 + 1) * ((c - 1) / 2 + 1) + (c / 2) * (c / 2) * (c / 2)
        };
        println!("{}", ans);
    } else {
        let c: usize = N / K;
        let ans = c * c * c;
        println!("{}", ans);
    }
}