import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] alpha = new int[26];
        for (char c : sc.next().toCharArray()) {
            alpha[c - 'A']++;
        }
        for (int x : alpha) {
            if (x > 1) {
                System.out.println("NO");
                return;
            }
        }
        System.out.println("YES");
    }
}