import qualified Data.ByteString.Char8 as BC
import Data.Maybe
import Data.List
import Data.Ord

readDoubles :: IO [Double]
readDoubles = map (fromIntegral . fst . fromJust . BC.readInt) . BC.words <$> BC.getLine

main :: IO ()
main = do
  getLine
  vs <- sortOn Down <$> readDoubles
  let calc a b = (a + b) / 2
  print $ foldr1 calc vs