using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Code
{
    class Program
    {
        static void Main(string[] args)
        {
            string E = Console.ReadLine();
            int i;
            if (E[0] != '1') { i = -1; }
            else
            {
                int len = E.Length;
                int t;
                for (t = 1; t < E.Length; t++)
                {
                    if (E[t] != '3') break;
                }
                if (t == E.Length) i = E.Length - 1;
                else i = -1;
            }

            Console.WriteLine(i);
        }
    }
}