import Data.List
import Control.Monad

fact n = product [1..n]

main = do
 n <- readLn
 as <- map read . words <$> getLine
 bs <- map read . words <$> getLine
 print (game n as bs)

game :: Int -> [Int] -> [Int] -> Double
game n as bs = (/ (fromIntegral ((fact n)^2))) $ fromIntegral $ length $ do
 as' <- permutations as
 bs' <- permutations bs
 guard $ length (filter id (zipWith (>) as' bs')) > div n 2
 return ()