using System;
using static System.Console;

public class Hello{
    public static void Main(){
        string word = ReadLine();
        char[] a = new char[30];
        int count =0;
        for(int i=0;i<word.Length;i++){
            count = 0;
            for(int j=0;j<30;j++){
                if(word[i] == a[j]){
                    count++;
                    break;
                }
            }
            if(count > 0){ break; }
            if(count == 0){
                a[i] = word[i];
            }
        }
        if(count >0){
            WriteLine("NO");
        }else{
            WriteLine("YES");
        }
    }
}