import java.util.*;
import java.util.Scanner;

public class Main {
	public static void main (String[] args) {
		Scanner in = new Scanner(System.in);
		String N = in.next();
        String w1 = N.substring(0, N.length()/2 );
        String w2 = N.substring(N.length()/2);
        
        if(N.length() % 2 != 0){
    		System.out.println("NO");
        }else if(w1.equals(w2)){
    		System.out.println("YES");            
        }else{
    		System.out.println("NO");
        }
   }

}