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: Time Limit Exceeded)

#[allow(dead_code)]
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()
}
#[allow(dead_code)]
fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn read_vec2<T: std::str::FromStr>(n: u32) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}
#[allow(dead_code)]
fn yn(result: bool) {
    if result {
        println!("Yes");
    } else {
        println!("No");
    }
}

fn main() {
    let v = read_vec::<i64>();
    let n = v[0];
    let k = v[1];

    let ks = n * 2 / k;
    let mut count = 0;
    for x in 1..ks+1 {
        for y in x..ks+1 {
            for z in y..ks+1 {
                if (x+y+z)*k % 2 != 0 {
                    continue;
                }
                let all = (x+y+z)*k/2;
                let a = all-y*k;
                let b = all-z*k;
                let c = all-x*k;
                //println!("{} {} {} => {} {} {}", x*k,y*k,z*k,a,b,c);
                if a > 0 && b > 0 && c > 0 &&
                    a <= n && b <= n && c <= n {
                    if a==b && b==c {
                        count += 1;
                    } else if a==b || b==c || c==a {
                        count += 3;
                    } else {
                        count += 6;
                    }
                }
            }
        }
    }
    println!("{}", count);
}