import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String str = sc.next();

        if (!(str.length() % 2 == 0)) {
            System.out.println("NO");
        } else if (str.substring(1, str.length() / 2).equals(str.substring(str.length() / 2 + 1))) {
            System.out.println("YES");
        } else {
            System.out.println("NO");
        }
    }
}