import scala.io.StdIn

object Main extends App {

  val n = StdIn.readLine().toInt
  private val a: Array[Int] = Array.ofDim(45)
  a(0) = 1
  a(1) = 1

  (2 to n).foreach{ i =>
    a(i) = a(i-1) + a(i-2)
  }
  
  println(a(n))
}
