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

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

solve :: [Int] -> Int
solve [f0, f1, n] = case n `mod` 3 of
                     0 -> f0
                     1 -> f1
                     2 -> f1 `xor` f0

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