fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s = s.trim().chars().collect::<Vec<_>>();
    let org = "abcdefghijklmnopqrstuvwxyz".chars().collect::<Vec<_>>();

    let i = (0..26).filter(|&i| s[i] != org[i]).nth(0).unwrap();
    println!("{}to{}", org[i], s[i]);
}