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

    let mut seen = vec![];
    for c in s.chars() {
        if seen.contains(&c) {
            println!("NO");
            return;
        }
        seen.push(c);
    }

    println!("YES");
}