import strutils, math
var N = stdin.readLine.parseInt
proc fibo(n : int) : int =
  var m = n.toFloat
  var
    t1 = pow(((1 + pow(5, 0.5)) / 2), m)
    t2 = pow(((1 - pow(5, 0.5)) / 2), m)
  result = round((t1 - t2) / pow(5, 0.5)).toInt
echo fibo(N+1)