import Data.List
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = breads >>= print . solve
    where
        [a, b, c]
            | a == b = c
            | b == c = a
            | otherwise = b
            
breads :: IO [Int]
breads = unfoldr uff <$> B.getLine
    where
        uff b = check <$> B.readInt b
        check (a, b)
            | B.null b = (a, b)
            | otherwise = (a, B.tail b)
