package main

import . "fmt"
import . "strings"

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 float64
		e,f=2,1
		for i:=0;i<1000;i++ {
			e/=2
			if i%2==0 &&x>0{
				continue
			}
			z+=float64(i+1)*f*(1-e)
			f*=e
		}
		Printf("%.12f\n",z)
	}
}