import java.util.Scanner

object Main extends App {
  val sc = new Scanner(System.in)
  val s = sc.next
  val hn = s.length / 2
  if (s.length % 2 == 0 && (0 until hn).forall(i => s(i) == s(i + hn))) {
    println("YES")
  } else {
    println("NO")
  }
}