fn main() {
    let mut xx = String::new();
    std::io::stdin().read_line(&mut xx).ok();
    let xx: Vec<&str> = xx.split_whitespace().collect();

    match xx[0].len().cmp(&xx[1].len()) {
        std::cmp::Ordering::Greater => println!("{}", xx[0]),
        std::cmp::Ordering::Less => println!("{}", xx[1]),
        std::cmp::Ordering::Equal => {
            for (a, b) in xx[0].chars().zip(xx[1].chars()) {
                match (a, b) {
                    ('4', '7') => println!("{}", xx[0]),
                    ('7', '4') => println!("{}", xx[1]),
                    (a, b) if a > b => println!("{}", xx[0]),
                    (a, b) if a < b => println!("{}", xx[1]),
                    _ => continue,
                }
                return;
            }
        }
    }
}