using System;
using System.Linq;

namespace GengaSort
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            int[] An = Console.ReadLine().Split(' ').Select(s => int.Parse(s)).ToArray();
            int count = N;
            for (int i = An.Length-1; i > -1; i--)
            {
                if (An[i] == count) count--;
            }
            Console.WriteLine(count);
        }
    }
}