import Control.Monad
import Text.Printf
import Data.List
import Data.Ratio

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

main :: IO()
main = do
  _ <- getLine
  v <- getInts
  let vs = sort v
  printf "%f" $ slv (drop 2 vs) ((vs !! 0 + vs !! 1) % 2)

slv :: [Int] -> Ratio Int -> Double
slv [] rat = (fromIntegral n) / (fromIntegral d)
  where d = denominator rat
        n = numerator rat
slv (s:sn) rat = slv sn $ (rat + (s % 1)) * (1 % 2)