import java.util.Scanner;

public class Main {

	@SuppressWarnings("resource")
	public static void main(String args[]) {
		Scanner scanner = new Scanner(System.in);
		int n=scanner.nextInt();
		String s=scanner.next();
		for(int i=1;i<=n;i++) {
			for(int j=i;j+(j+1-i)<=n;j++) {
				String a=s.substring(i-1,j);
				String b=s.substring(j,j+(j+1-i));
				if(a.equals(b)) {
					System.out.println("YES");
					return;
				}
			}
		}
		System.out.println("NO");
	}
}