import Data.Ratio
import Text.Printf

a :: [Ratio Integer]
a = 4 : 3 : map (* (1 % 4)) (zipWith (+) (map (* (- 12)) a) (map (* 19) (tail a)))

main = do
  n <- readLn
  let
    r = a !! n
    nu = fromIntegral $ numerator r
    de = fromIntegral $ denominator r
   in printf "%.12f\n" (nu / de :: Double)