import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char[] arr = sc.next().toCharArray();
        boolean[] used = new boolean[26];
        for (char c : arr) {
            int x = c - 'A';
            if (used[x]) {
                System.out.println("NO");
                return;
            }
            used[x] = true;
        }
        System.out.println("YES");
   }
}