using System.Collections.Generic;
using System;

public class Hello
{
    public static void Main()
    {
        var hs = new HashSet<char>();
        var s = Console.ReadLine().Trim();
        for (int i = 0; i < s.Length; i++)
            if (!hs.Add(s[i])) { Console.WriteLine("NO"); goto end; }
        Console.WriteLine("YES");
        end:;
    }
}