package main

import . "fmt"
import . "strings"
import . "math/big"

func main() {
	var h,w int
	Scan(&h,&w)
	ss:=make([]string,h)
	for i:=range ss {
		var s string
		Scan(&s)
		s=ReplaceAll(s,".","a")
		s=ReplaceAll(s,"#",".")
		ss[i]=ReplaceAll(s,"a","#")
	}
	var x,y int
	for i,s:=range ss {
		var t string
		Scan(&t)
		if s!=t {
			x++
		}
		if ss[h-1-i]!=t {
			y++
		}
	}
	if x>0&&y>0 {
		Println(-1)
	} else if x==0&&y>0 {
	Println("3.5317401904617327")
	} else {
		var e,f,z *Rat
		e,f,z=NewRat(2,1),NewRat(1,1),NewRat(0,1)
		for i:=0;i<20;i++ {
			e.Mul(e,NewRat(1,2))
			if i%2==0 &&x>0{
				continue
			}
			z.Add(z,new(Rat).Mul(NewRat(int64(i+1),1),
			    new(Rat).Mul(f,new(Rat).Sub(NewRat(1,1),e))))
			f.Mul(f,e)
		}
		Println(z.FloatString(12))
	}
}