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

    let original: Vec<char> = ('a'..='z').collect();
    let i = (0..s.len()).find(|&i| s[i] != original[i]).unwrap();

    println!("{}to{}", original[i], s[i]);
}