import java.util.*; class Main { static Scanner sc = new Scanner(System.in); public static void main(String[] args) { String s = sc.next(); String ans = "YES"; if (s.length()%2 != 0) ans = "NO"; else { if (!s.substring(0,s.length()/2).equals(s.substring(s.length()/2,s.length()))) { ans = "NO"; } } System.out.println(ans); } }