use std::collections::HashSet;

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

    if candidates.len() >= 12 {
        if candidates.len() == 13 {
            TARGETS.iter().for_each(|c| {
                println!("{}", c);
            });
        } else {
            println!("{}", TARGETS.iter().find(|c| !candidates.contains(c)).unwrap());
        }
    } else {
        println!("Impossible");
    }
}