package no290;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		String s = sc.next();
		if (s.contains("00") || s.contains("11") || s.contains("0101") || s.contains("1010")) {
			System.out.println("YES");
		}else{
			System.out.println("NO");
		}
	}

}