import java.util.*; import java.io.*; import java.math.*; public class No290 { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n = sc.nextInt(); String s = sc.next(); if(s.length() < 2) { System.out.println("NO"); return; } for(int i = 0; i < n; i++) { for(int j = i; j < n; j++) { if(j+(j+1-i) < n) { String m = s.substring(i, j+1); String a = s.substring(j+1, j+(j+1-i)+1); if(m.equals(a)) { System.out.println("YES"); return; } } } } System.out.println("NO"); } }