using System;

namespace No290
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			var n = Convert.ToInt32(Console.ReadLine ());
			var s = Console.ReadLine ();
			if (n == 1) 
			{
				Console.WriteLine ("NO");
				return;
			}
			if (n == 2) 
			{
				if(s.Equals("01"))
				{
					Console.WriteLine ("NO");
					return;
				}
				if(s.Equals("10"))
				{
					Console.WriteLine ("NO");
					return;
				}
			}
			if (n == 3) 
			{
				if(s.Equals("010"))
				{
					Console.WriteLine ("NO");
					return;
				}
				if(s.Equals("101"))
				{
					Console.WriteLine ("NO");
					return;
				}
			}
			Console.WriteLine("YES");
		}
	}
}