fn main() {
    let stdin = std::io::read_to_string(std::io::stdin()).unwrap();
    let mut stdin = stdin.split_ascii_whitespace();

    let s: String = stdin.next().unwrap().parse().unwrap();

    println!("{}", output(solve(s)));
}

fn solve(s: String) -> bool {
    let mut is_appeared = [false; 128];
    s.bytes().all(|s| {
        let ret = !is_appeared[s as usize];
        is_appeared[s as usize] = true;
        ret
    })
}

fn output(ans: bool) -> &'static str {
    match ans {
        true => "YES",
        false => "NO",
    }
}