object Main extends App {
  val in = scala.io.Source.stdin.getLines.toSeq
  //val ls = in(0).split(' ').map(_.toInt)
  val str = in(0)
  val len = str.size
  val ret = (0 until len/2).count(i => str(i)!=str(len-i-1) )
  println(ret)
}
