class Program
{
    static void Main(string[] args)
    {
        string[] inputNum = Console.ReadLine()!.Split(' ');

        for (int i = 1; i <= 10; i++)
        {
            bool judg = false;

            for (int j = 0; j < inputNum.Length; j++)
            {
                if (inputNum[j] == i.ToString())
                {
                    judg = true;
                }
            }

            if (!judg)
            {
                Console.WriteLine(i);
                break;
            }
        }
    }
}