import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        char[] arr = sc.next().toCharArray();
        if (arr.length % 2 == 0) {
            for (int i = 0; i < arr.length / 2; i++) {
                if (arr[i] != arr[arr.length / 2 + i]) {
                    System.out.println("NO");
                    return;
                }
            }
        } else {
            System.out.println("NO");
            return;
        }
        System.out.println("YES");
    }
}