import java.util.Scanner;

public class Test {
	public static Scanner sc = new Scanner(System.in);

	public static void main(String[] args) {
		int n = sc.nextInt();
		String s = sc.next();
		for(int i = 0; i < n-1; i++){
			for(int j = i+1; j < n && 2*j-i <= n; j++){
				if(s.substring(i, j).equals(s.substring(j, 2*j-i))){
					System.out.println("YES");
					return;
				}
			}
		}
		System.out.println("NO");
	}
}