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)

// -*- coding:utf-8-unix -*-
use std::cmp;
use std::collections::BTreeMap;
use std::collections::BTreeSet;
use std::collections::BinaryHeap;
use std::collections::HashMap;
use std::collections::HashSet;
use std::collections::LinkedList;
use std::collections::VecDeque;
use std::fs::File;
use std::io;
use std::io::prelude::*;
use std::vec;

const INF: i64 = 1223372036854775807;
const MEM_SIZE: usize = 202020;

macro_rules! input {
    (source = s:expr, $(r:tt)*) => {
        let mut iter = s.split_whitespace();
        let mut next = || { iter.next().unwrap() };
        input_inner!{next, $(r)*}
    };
    ($(r:tt)*) => {
        let stdin = std::io::stdin();
        let mut bytes = std::io::Read::bytes(std::io::BufReader::new(stdin.lock()));
        let mut next = move || -> String{
            bytes
                .by_ref()
                .map(|r|r.unwrap() as char)
                .skip_while(|c|c.is_whitespace())
                .take_while(|c|!c.is_whitespace())
                .collect()
        };
        input_inner!{next, $(r)*}
    };
}

macro_rules! input_inner {
    (next:expr) => {};
    (next:expr, ) => {};

    (next:expr, var:ident : t:tt $(r:tt)*) => {
        let var = read_value!(next, t);
        input_inner!{next $(r)*}
    };
}

macro_rules! read_value {
    (next:expr, ( $(t:tt),* )) => {
        ( $(read_value!(next, t)),* )
    };

    (next:expr, [ t:tt ; len:expr ]) => {
        (0..len).map(|_| read_value!(next, t)).collect::<Vec<_>>()
    };

    (next:expr, chars) => {
        read_value!(next, String).chars().collect::<Vec<char>>()
    };

    (next:expr, usize1) => {
        read_value!(next, usize) - 1
    };

    (next:expr, t:ty) => {
        next().parse::<t>().expect("Parse error")
    };
}

use std::cmp::*;
use std::collections::*;
use std::io::stdin;
use std::io::stdout;
use std::io::Write;

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

#[allow(unused_macros)]
macro_rules! p {
    ([$($x:expr), *]) => {{
        let mut f = true;
        $(
            print!("{}{}", if f {""} else {" "}, $x);
            f = false;
        )*
        print!("\n");
    }};
    ($x:expr) => {{
        let mut f = true;
        for a in $x.iter() {
            print!("{}{}", if f {""} else {" "}, a);
            f = false;
        }
        print!("\n");
    }};
}

fn readii() -> (i64, i64) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<i64>().unwrap(),
        iter.next().unwrap().parse::<i64>().unwrap(),
    )
}

fn readuu() -> (usize, usize) {
    let mut str = String::new();
    let _ = stdin().read_line(&mut str).unwrap();
    let mut iter = str.split_whitespace();
    (
        iter.next().unwrap().parse::<usize>().unwrap(),
        iter.next().unwrap().parse::<usize>().unwrap(),
    )
}

fn solve() {
    let (n, k) = readuu();
    let mut vec: Vec<i64> = vec![0; MEM_SIZE];
    for i in 1..n + 1 {
        let mut x = (i % k);
        vec[x] += 1;
    }
    let mut res: i64 = 0;
    res += vec[0] * vec[0] * vec[0];
    if k % 2 == 0 {
        res += vec[k / 2] * vec[k / 2] * vec[k / 2];
    }
    println!("{:?}", res);
}
fn main() {
    solve()
}