using System;
using System.Collections.Generic;

namespace MobProgramming
{
    class JengaSort
    {
        private static List<Int32> _ryoList = new List<Int32>();

        static void Main()
        {
            Int32 length = Int32.Parse(Console.ReadLine());
            String[] s = Console.ReadLine().Split(' ');
            Initialize(s);
            Console.WriteLine(CountRyo(length));

        }

        static void Initialize(String[] strArray)
        {
            foreach (var str in strArray)
            {
                _ryoList.Add(Int32.Parse(str));
            }
        }

        static Int32 CountRyo(Int32 num)
        {
            if (_ryoList.IndexOf(num) > _ryoList.IndexOf(num - 1))
            {
                var result = CountRyo(num - 1);
                return result;
            }
            return num - 1;
        }
    }
}