{-# LANGUAGE OverloadedStrings #-}
module Main where

import Data.Maybe
import qualified Data.ByteString.Char8 as C
import Control.Monad(forM_)
import Data.Int
import Data.List
import Data.Array
import Data.Word
import Data.Bits
import qualified Data.IntMap as IntMap
import qualified Data.Map as Map

yes :: C.ByteString
yes = "YES"

no :: C.ByteString
no = "NO"

getInts :: IO [Int]
getInts = do
  ss <- C.getLine
  return $ map (fst . fromJust . C.readInt) $ C.words ss

getIntss :: Int -> IO [[Int]]
getIntss 0 = return []
getIntss n = do
  xs <- getInts
  xss <- getIntss (n - 1)  
  return $ xs : xss

-- end standard template --

main :: IO ()
main = do
  [n] <- getInts
  xs <- getInts
  ys <- getInts
  let res = solve n xs ys
  print res

solve :: Int -> [Int] -> [Int] -> Double
solve n xs ys = (sum $ map eval zs) / (realToFrac $ length zs)
  where
    zs = [zip xs' ys' | xs' <- permutations xs, ys' <- permutations ys]
    eval :: [(Int,Int)] -> Double
    eval ws = let (s1, s2) = eval' ws (0,0) in if s1 > s2 then 1.0 else 0.0
    eval' :: [(Int,Int)] -> (Int, Int) -> (Int, Int)
    eval' [] t = t
    eval' ((w1,w2):ws) (s1, s2) = case compare w1 w2 of
                                  LT -> eval' ws (s1, s2 + 1)
                                  EQ -> eval' ws (s1, s2)
                                  GT -> eval' ws (s1 + 1, s2)