use std::collections::HashSet;

fn main() -> Result<(), std::io::Error> {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let input_str = s.trim();

    let uniq: HashSet<char> = input_str.chars().into_iter().collect();

    if input_str.len() == uniq.len() {
        println!("{}", "YES");
    } else {
        println!("{}", "NO");
    }

    Ok(())
}