fn best_fuel(x: &str, y: &str) -> &str {
    if x.len() > y.len() {
        x
    } else {
        y
    }
}

fn main() {
    let result;
    let propellant1 = String::from("RP-1");
    let propellant2 = String::from("LNG");
    result = best_fuel(&propellant1, &propellant2);
    println!("result is {}", result);
}