{-# OPTIONS_GHC -Wall #-}

import Data.Array

readInt :: String -> Int
readInt = read

fibs :: Array Int Int
fibs = listArray (0,50) $ 1 : 1 : [f i | i <- [2..50]]
    where
        f i = fibs!(i-1) + fibs!(i-2)

main :: IO ()
main = do
    n <- fmap readInt getLine

    let ans = fibs ! n

    print ans

