using System;
using System.Linq;

namespace _08.EvenNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            string str = Console.ReadLine();

            str = str.Remove(str.Trim().Length - 1);

            string[] input = str
                .Split()
                .ToArray();

            int[] result = input
                .Where(x => x.All(char.IsDigit))
                .Select(int.Parse)
                .Where(x => x % 2 == 0)
                .ToArray();

            if (result.Length == 0)
            {
                Console.WriteLine(-1);
            }
            else
            {
                int number = result
                    .Max();
                Console.WriteLine(number);
            }

        }
    }
}