class Program
    {
        static void Main(string[] args)
        {
            const string sample = "abcdefghijklmnopqrstuvwxyz";
            string str = Console.ReadLine();
            for(int i = 0 ; i < 26; i++)
            {
                if (sample[i] != str[i])
                {
                    Console.WriteLine(sample[i] + "to" + str[i]);
                    break;
                }
            }
        }
    }