import Data.Bits
import Data.Word
main = getLine >>= print . solve . map read . words

solve :: [Word64] -> Word64
solve [f0, f1, n]
        | n == 0 = f0
        | n == 1 = f1
        | otherwise = snd $ foldl (\(b2, b1) x -> (b1, xor b1 b2)) (f1, xor f0 f1) [3..n]