import Data.Bits (xor, Bits)
import Control.Applicative ((<$>))

xorFibonacci :: (Bits a, Integral a) => a -> a -> [a]
xorFibonacci a1 a2 = seq a1 $ (:) a1 $ xorFibonacci a2 $ xor a1 a2

main :: IO ()
main = do
    (f0 : f1 : n : _) <- words <$> getLine
    let [f0', f1'] = map read [f0, f1] :: [Integer]
    let n' = read n :: Int
    print $ head $ drop n' $ xorFibonacci f0' f1'