import java.util.*; public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); String s = sc.nextLine(); if (s.length() % 2 == 1) { System.out.println("NO"); System.exit(0); } String[] a = new String[s.length() / 2]; String[] b = new String[s.length() / 2]; for (int i = 0; i < s.length() / 2; i++) { a[i] = String.valueOf(s.charAt(i)); } for (int j = 0; j < s.length() / 2; j++) { b[j] = String.valueOf(s.charAt(s.length() / 2 + j)); } int flg = 0; for (int k = 0; k < s.length() / 2; k++) { if (a[k].equals(b[k])) { flg += 1; } } if (flg == s.length() / 2) { System.out.println("YES"); } else { System.out.println("NO"); } sc.close(); /* for (String v : a) { System.out.print(v); } System.out.println(); for (String v : b) { System.out.print(v); } */ } }