using System;
public class Program
{
    public static void Main()
    {
        //int num = int.Parse(Console.ReadLine() ?? string.Empty);
        string[] pass = (Console.ReadLine() ?? string.Empty).Trim().Split(' ');
        //string a = Console.ReadLine() ?? string.Empty;
        //string b = Console.ReadLine() ?? string.Empty;

        for (int i = 1;i <= 10;i++)
        {
            if (int.Parse(pass[i-1]) != i)
            {
                Console.WriteLine(i);
                break;
            }
        }
    }
}