fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s = s.trim();
    let a = "abcdefghijklmnopqrstuvwxyz";

    let b = s.chars().into_iter().zip(a.chars());
    for x in b {
        if x.0 != x.1 {
            println!("{}to{}", x.1, x.0);
            return;
        }
    }
}