import java.util.*;

public class Main {

    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        String s = sc.next();
        if(judge(s)) {
            System.out.println("YES");
        } else{
            System.out.println("NO");
        }
    }
    
    static boolean judge(String s) {
        String str = s.substring(0, s.length()/2);
        s = s.replace(str, "");
        if(s.equals("")) {
            return true;
        }
        return false;
    }
}