using System;
using System.Linq;
using System.Collections.Generic;

namespace test20190423
{
    class Program
    {
        static void Main(string[] args)
        {
            var ss = Console.ReadLine().Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries).Select(x => int.Parse(x));
            Console.WriteLine(Enumerable.Range(1, 10).Except(ss).First());
            Console.ReadLine();
        }
    }
}