using System;

public class Hello
{
    static void Main()
    {
        Console.ReadLine();
        var s = Console.ReadLine().Trim();
        getAns(s);
    }
    static bool calc(string s, string t) => s.IndexOf(t) != -1;
    static void getAns(string s)
    {
        if (calc(s, "00")) { Console.WriteLine("YES"); return; }
        if (calc(s, "11")) { Console.WriteLine("YES"); return; }
        Console.WriteLine("NO");
    }
}