fn main() {
    let stdin = std::io::read_to_string(std::io::stdin()).unwrap();
    let mut stdin = stdin.split_ascii_whitespace();

    let s: String = stdin.next().unwrap().parse().unwrap();

    println!("{}", output(solve(s)));
}

fn solve(s: String) -> (u8, u8) {
    "abcdefghijklmnopqrstuvwxyz"
        .bytes()
        .zip(s.bytes())
        .find(|(a, b)| a != b)
        .unwrap()
}

fn output(ans: (u8, u8)) -> String {
    String::from(ans.0 as char) + "to" + &String::from(ans.1 as char)
}