import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Tester {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String str = br.readLine();

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