const S: &str = "abcdefghijklmnopqrstuvwxyz";
fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    for (i, c) in S.chars().enumerate() {
        let si = s.chars().nth(i).unwrap();
        if c != si {
            println!("{}to{}", c, si);
            return;
        }
    }
}