using System;

class Program
{
    static void Main()
    {
        int n = int.Parse(Console.ReadLine());
        string s = Console.ReadLine();

        if (n >= 4)
        {
            Console.WriteLine("YES");
            return;
        }

        if (s.Contains("00") || s.Contains("11"))
            Console.WriteLine("YES");
        else
            Console.WriteLine("NO");
    }
}