object Main {
  def main(args: Array[String]): Unit = {
    import scala.io.StdIn.readLine

    val s = readLine()
    val n = s.length

    if (n % 2 == 0 && s.take(n / 2) == s.takeRight(n / 2)) {
      println("YES");
    } else {
      println("NO");
    }
  }
}