import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();
        int length = str.length()/2;
        if(str.substring(0, length) == str.substring(length)) {
            System.out.println("YES");
        }else{
            System.out.println("NO");
        }
    }
}