{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BinaryLiterals #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE NumDecimals #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}
{-# LANGUAGE FlexibleContexts #-}

{-# OPTIONS_GHC -O2 #-}
{-# OPTIONS_GHC -Wno-tabs #-}

import Control.Applicative
import Control.Arrow
import Control.Monad
import Control.Monad.ST

import Data.Char
import Data.List
import Data.Maybe

import qualified Data.ByteString.Char8 as B

import Data.Array
import Data.Array.ST.Safe
import Data.STRef

import Debug.Trace
import Text.Printf

readInt = readLn :: IO Int
readInteger = readLn :: IO Integer
readInts = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine
readIntegers = map ( fst . fromJust . B.readInteger ) . B.words <$> B.getLine

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

modifyArray a i f = writeArray a i =<< f <$> readArray a i

printList [] = putChar '\n'
printList [a] = print a
printList (a:as) = putStr ( show a ) >> putChar ' ' >> printList as

main = do
	[ h, w ] <- readInts
	[ ss, ts ] <- replicateM 2 $ replicateM h getLine
	let
		es :: Maybe [Double] = case ( match ss ts, match ( rev ss ) ts ) of
			( True, True ) -> Just $ f 1 [ 0 .. ]
			( True, False ) -> Just $ f 1 [ 0, 2 .. ]
			( False, True ) -> Just $ f 1 [ 1, 3 .. ]
			( False, False ) -> Nothing
	case es of
		Just es -> printf "%.12f\n" $ sum $ take 100000 es
		otherwise -> print (-1)

rev = reverse . map reverse

match ss ts = and $ zipWith match' ss ts
	where
	match' s t = and $ zipWith (/=) s t

f _ [] = []
f p (i:is) = ( i + 1 ) * p * p' : f ( p * ( 1 - p' ) ) is
	where
	p' = 1 - ( 2 ** (-i) )