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);
        }
        */
    }
}