import Control.Applicative ((<$>))

main :: IO ()
main = solve <$> readLn >>= print

solve :: Int -> Double
solve k = head . (!! k) $ iterate f (replicate 6 0.0)
  where f :: [Double] -> [Double]
        f xs = let xs6 = take 6 xs
               in (sum xs6 / 6.0 + 1.0) : xs6