using System;
class Program {
    static void Main() {
        int n = int.Parse(Console.ReadLine());
        string s = Console.ReadLine();
        int maxW = n / 2;
        for (int w = 1; w <= maxW; w++) {
            int tmp = n - 2 * w;
            for (int i = 0; i <= tmp; i++) {
                if (s.Substring(i, w) == s.Substring(i + w, w)) {
                    Console.WriteLine("YES");
                    return;
                }
            }
        }
        Console.WriteLine("NO");
    }
}