import Data.Bits
import Data.List
import Control.Monad
import qualified Data.Vector.Unboxed as V
import qualified Data.Vector.Unboxed.Mutable as VM
import Control.Monad.ST
import Data.Maybe (fromMaybe)
import qualified Data.ByteString.Lazy.Char8 as B
--import Debug.Trace

main :: IO ()
main = do
  n <- readLn :: IO Double
  as <- map read.words <$> getLine :: IO [Double]
  print $ product as / sum [ product as / a | a <- as]
