import java.io.*;
import java.util.*;
import java.math.*;

class Main {
	
	public static void out (Object o) {
		System.out.println(o);
	}
	
	public static boolean solve (String s , int n) {
		if (n == 1) return false;
		if (n == 2) return !s.equals("01") && !s.equals("10");
		if (n == 3) return !s.equals("010") && !s.equals("101");
		return true;
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		int n = Integer.parseInt(br.readLine());
		String s = br.readLine();
		
		out(solve(s , n) ? "YES" : "NO");
	}
	
}