import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T

main :: IO ()
main = do
  (l : _) <- map unsafeTextToDouble . T.words <$> T.getLine :: IO [Double]
  print $ l ^ 3 / 27

unsafeTextToDouble :: T.Text -> Double
unsafeTextToDouble s = case T.double s of
  Right (x, _) -> x
