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;

            for (int i = 0; i < number1.Length; i++)
            {
               number2[i] = int.Parse(number1[i]);
               ans += 1;
                if (number2[i] != i + 1)
                {
                    break;
                }
                else if (number2[i] == i + 1)
                {
                    ans = 10;
                }
            }

            //表示
            Console.WriteLine(ans);

        }
    }
}