import java.util.Scanner; // https://yukicoder.me/problems/no/739 public class TwoTimes739 { public static void main(String[] args) { // 標準入力から読み込む際に、Scan Scanner sc = new Scanner(System.in); // String 1つ分を読み込む String s = sc.next(); String s1 = s.substring(0, s.length() / 2); String s2 = s.substring(s.length() / 2 + 1, s.length()); if (s1.equals(s2)) { System.out.println("YES"); } else { System.out.println("NO"); } } }