import math._

object Main {
  def calc(n: Int): Long = {
    val dp = new Array[Long](n+1)
    dp(0) = 1
    dp(1) = 1
    for (i <- 2 to n) {
      dp(i) = dp(i-1) + dp(i-2)
    }
    dp(n)
  }

  def main(args: Array[String]) {
    val sc = new java.util.Scanner(System.in)
    val n = sc.nextInt
    println(calc(n))
  }
}