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

namespace Algorithm
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = int.Parse(Console.ReadLine());
            var a = Console.ReadLine().Split().Select(int.Parse).ToArray();

            var continuous = new List<int>();
            var cur = a[0];
            var count = 1;
            for (var i = 1; i < n; i++)
            {
                if (cur == a[i])
                    count++;
                else
                {
                    continuous.Add(count);
                    count = 1;
                }

                cur = a[i];
            }
            continuous.Add(count);

            var dp = new int[continuous.Count];
            dp[0] = continuous[0];
            for (var i = 1; i < continuous.Count; i++)
            {
                dp[i] = Math.Max(dp[i], dp[i - 1] + continuous[i] - 1);
                if (i > 1) dp[i] = Math.Max(dp[i], dp[i - 2] + continuous[i]);
            }

            Console.WriteLine(dp[continuous.Count - 1]);
        }
    }
}