import java.util.*;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int n = sc.nextInt();
		String in = sc.next();
		if(in.length()>=4) System.out.println("YES");
		else if(in.length()==1) System.out.println("NO");
		else{
			for(int i=0;i<in.length()-1;i++){
				if(in.charAt(i)==in.charAt(i+1)){
					System.out.println("YES");
					return;
				}
			}
			System.out.println("NO");
		}
		
	}
}