import Control.Applicative ((<$>))
import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T
import Text.Printf (printf)

unsafeReadDec:: Integral a => T.Text -> a
unsafeReadDec t = case T.decimal t of
    Right x -> fst x
    Left e -> error e

computeMax :: (Integral a, RealFloat b) => [a] -> a -> b
computeMax ls k = bis eps maxLength
    where
        eps = 10.0 ** (-9)
        maxLength = 10.0 ** 9
        bis low high
            | high - low <= eps || (high - low) / low <= eps = mid
            | n >= k = bis mid high
            | otherwise = bis low mid
            where
                mid = (high + low) / 2
                n = sum $ fmap (floor . (/ mid) . fromIntegral) ls

main :: IO ()
main = do
    _ <- T.getLine
    ls <- fmap unsafeReadDec . T.words <$> T.getLine :: IO [Int]
    k <- unsafeReadDec <$> T.getLine :: IO Int
    printf "%.16f\n" (computeMax ls k :: Double)