solve :: Int -> Int
solve n =
  aux n
  where
    aux 0 = 1
    aux 1 = 1
    aux n = auxList !! (n - 1) + auxList !! (n - 2)
    auxList = [aux n | n <- [0,1..]]

main :: IO ()
main = do
  n <- (read :: String -> Int) <$> getLine
  (putStr . show . solve) n