main :: IO ()
main = do
  input <- promptLine "Skriv inn h: "
  let h = read input :: Double
  putStrLn $ show $ tetraederVolum h

promptLine :: String -> IO String
promptLine prompt = do
  putStr prompt
  getLine

tetraederVolum :: Double -> Double
tetraederVolum h = sqrt 2 * a / 12
  where a = 3 / sqrt 6 * h