import java.util.Scanner;

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