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","#")
	}
	for _,s:=range ss {
		var t string
		Scan(&t)
		if s!=t {
			Println(-1)
			return
		}
	}
	Println("3.5317401904617327")
}