import scala.io.StdIn

object Main {
  def main(args: Array[String]): Unit = {
    val n = StdIn.readInt

    val dp: Array[Long] = Array.fill(n + 1)(0)
    dp(0) = 1

    for (i <- (0 until n); j <- (1 to 2)) {
      if (i + j <= n) {
        dp(i + j) += dp(i)
      }
    }

    println(dp(n))
  }
}