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

main :: IO ()
main = do
  solve <$> getl (map read . words) >>= print

solve :: [Int] -> Int
solve [f0, f1, n] = f f0 f1 0
  where
    f x y z = if z == n then x else f y (x `xor` y) (z + 1)

getl :: (String -> a) -> IO a
getl f = f <$> getLine