{-
fibonacci :: Int -> Int
fibonacci = fibo (1, 1) 2
    where
      fibo :: (Int, Int) -> Int -> Int -> Int
      fibo (pp, prev) pos n
          | n < 2 = 1
          | pos >= n = pp + prev
          | otherwise = fibo (prev, pp+prev) (pos+1) n
-}

fibonacci :: Int -> Int
fibonacci n
    | n < 2 = 1
    | otherwise = (fibonacci (n-1)) + (fibonacci (n-2))

main :: IO ()
main = do
  n <- readLn
  putStrLn $ show $ fibonacci n