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

namespace PracticeAtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
			
			//1-10
			string sC = Console.ReadLine();
			string[] sD = sC.Split(' ');
			int[] after = sD.Select(s => int.Parse(s)).ToArray();
			
			int flg = 0 ;
			int intA = 0;
			int intB=0;
			
			for(int i=0; i<9;i++){
				intA = after[i];
				intB = i+1;
				if(intA != intB){
					flg = i+1;
					Console.WriteLine(flg);
					break;
				
				}
			}
			
			
		}
    }
}