{-# OPTIONS_GHC -O2 #-}
import qualified Text.Printf           as Text

readInt = readLn :: IO Int

f :: Fractional b =>  Int -> a
f n = fromIntegral (n ^ 3)

main :: IO ()
main = do
  l <- readInt
  let x = (f l) / 9.0
  Text.printf "%.8f" x