Collatz Conjecture in Rust

collatz.rs

// Responsible for calcule Collatz Conjecture
// n -> n/2 (if n is pair) n -> 3n + 1 (if n is odd)
//

fn calcule(num: u64) -> u64 {
    if num <= 1 { return 1; };
    if num % 2 == 0 {
        num / 2
    } else{
        3 * num + 1
    }
}

fn collatz(num: u64, step: u64) -> u64 {
    let res = calcule(num);
    if res == 1 {
        step + 1
    } else { 
        collatz(res, step + 1)
    }
}

fn main() {
    let mut max_num: u64 = 0;
    let mut max_steps: u64 = 0;
    for i in 1..1000000 {
        let steps = collatz(i, 1);

        if max_steps < steps {
            max_steps = steps;
            max_num = i;
        }
    }
    println!("Result num: {} in {} steps", max_num, max_steps);
}

Thanks!