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

class Program
{
    public void Solve()
    {
        int[] B = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();

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

    static void Main()
    {
        var solver = new Program();
        solver.Solve();
    }
}