import java.util.Scanner;
import java.lang.StringBuilder;
  
  public class Main {
       public static void main(String[] args) {
           Scanner sc = new Scanner(System.in);
  
           String s = sc.nextLine();
           StringBuilder sb = new StringBuilder(s);

           int k = sb.length();
           String s1 = sb.substring(0,k/2);
           String s2 = sb.substring(k/2,k);

           if(s1.equalsIgnoreCase(s2)){
               System.out.println("YES");
           }else{
               System.out.println("NO");
           }
       }
   }