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