using System;

class Program
{
    static void Main(string[] args)
    {
        var S = Console.ReadLine();
        var e = "abcdefghijklmnopqrstuvwxyz";
        char a = '\0';
        char b = '\0';
        bool flag = false;

        for (int i = 0; i < 26; i++)
        {
            if (S[i] != e[i])
            {
                a = e[i];
                b = S[i];
                flag = true;
                break;
            }
        }
        if (flag == true) Console.WriteLine("{0}to{1}", a, b);
    }
}