object Main extends App {
  val n = readLine.toInt
  
  var list = scala.collection.mutable.Seq[Long](2,1)
  
  for (i <- 1 to n - 1) {
    val a = list.reverse.head + list.dropRight(1).reverse.head
    list = list :+ a
  }
  
  println(list.reverse.head)
}