fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    let s = s.trim().chars().map(|c| c as usize - 'A' as usize).collect::<Vec<_>>();

    let mut cnts = vec![0usize; 26];
    for &v in s.iter() { cnts[v] += 1; }
    if cnts.iter().filter(|&&v| v > 1).count() == 0 {
        println!("YES");
    } else {
        println!("NO");
    }
}