module Main where

import Data.List

main :: IO ()
main = do
  { [n] <- getInts
  ; xs  <- getInts
  ; print $ av $ snd3 $ foldl f ([],[],[]) xs
  }
  where
    f y x = case y of
      (ls,[m],rs)
        | x < m     -> case insertBy (flip compare) x ls of
            l:ls'     -> (ls',[l,m],rs)
        | otherwise -> case insert x rs of
            r:rs'     -> (ls,[m,r],rs')
      (ls,[m,n],rs)
        | x < m     -> (insertBy (flip compare) x ls,[m],n:rs)
        | x < n     -> (m:ls,[x],n:rs)
        | otherwise -> (m:ls,[n],insert x rs)
      (_,[],_)      -> ([],[x],[])

getInts :: IO [Int]
getInts = map read . words <$> getLine

snd3 :: (a,b,c) -> b
snd3 (_,b,_) = b 

av :: [Int] -> Double
av [x]   = fromIntegral x
av [x,y] = fromIntegral (x + y) / 2