using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace No481OnetoTen
{
    class Program
    {
        static void Main(string[] args)
        {
            //値の入力
            string[] number1 = Console.ReadLine().Split(' ');
            int[] number2 = new int[number1.Length];
            
            int ans = 0; //抜けてる数字をカウントするためのもの

            for (int i = 0; i < number1.Length; i++)
            {
               number2[i] = int.Parse(number1[i]);
               ans += 1;
                //10が漏れてる場合
                if (number2[8] == 9)
                {
                    Console.WriteLine(ans+1);
                    break;
                }
                //1～9のいずれかが漏れてる場合
                else if (number2[i] != i + 1)
                {
                    Console.WriteLine(ans);
                    break;
                }
            }
        }
    }
}