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

class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int mojiCount = int.Parse(Reader.ReadLine());
        string inpt = Reader.ReadLine();
        bool ans = true;
        if (inpt.Length == 1)
        {
            ans = false;
        }
        else if (inpt.Length == 2)
        {
            if (inpt[0] == inpt[1])
            {
                ans = true;
            }
            else
            {
                ans = false;
            }

        } else if(inpt.IndexOf("00") >= 0 || inpt.IndexOf("11") >= 0) {
            ans = true;
        }
        else
        {
            ans = this.Hantei(inpt, "0");
            if (!ans)
            {
                ans = this.Hantei(inpt, "1");
            }
        }

        Console.WriteLine(ans ? "YES" : "NO");

    }

    private bool Hantei(string inpt, string delimiter)
    {
        string[] keyList = new string[] { delimiter + "0", delimiter + "1" };

        foreach (string key in keyList)
        {
            string[] splt = inpt.Split(new string[] { key }, StringSplitOptions.None);
            if (splt.Length >= 3)
            {
                List<string> items = splt.ToList();
                items.RemoveAt(0);

                for (int i = 1; i < items.Count; i++)
                {
                    if (items[i - 1].Equals(items[i]))
                    {
                        return true;
                    }
                }
                items.Sort();
                for (int i = 1; i < items.Count; i++)
                {
                    if (items[i - 1].Equals(items[i]) && this.Hantei(inpt, key))
                    {
                        return true;
                    }
                }
            }
        }
        return false;


    }



    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"
 
3
000
 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }

    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}