main :: IO ()
main = readLn >>= print . solve

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