class Program
{
    static void Main(string[] args)
    {
        string word = Console.ReadLine()!;
        int count = 0;

        for (int i = 0; i < word.Length; i++)
        {
            for (int j = 0; j < word.Length; j++)
            {
                if (word[i] == word[j])
                {
                    count++;
                }
            }
        }

        if (count == word.Length)
        {
            Console.WriteLine("YES");
        }
        else
        {
            Console.WriteLine("NO");
        }
    }
}