package algo;

import java.util.Scanner;

public class sample7 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		String S = sc.next();
		if(S.length() % 2 == 1) {
			System.out.println("NO");
		}
		else {
			String ss = S.substring(S.length() / 2);
			String sss = S.substring(0, S.length() / 2);
			if(sss.equals(ss)) {
				System.out.println("YES");
			}
			else {
				System.out.println("NO");
			}
		}
	}
}