object Main {
	def main(A:Array[String]){
		val s = new java.util.Scanner(System.in)
		type T=Long
		def g(v:(T,T)) = (v._2,v._1+v._2)
		def f(i:T):(T,T) =if(i<2)(1,1) else g(f(i-1))
		println(f(s.nextInt)._2)
	}
}