def main():
	import sys
	input = lambda : sys.stdin.readline().rstrip()
	MI = lambda : map(int, input().split())
	INF = 1<<60
	
	H,W = MI()
	ma = [input() for i in range(H)]
	fe = [input() for i in range(H)]
	
	def check(T, S):
		for i in range(H):
			for j in range(W):
				if T[i][j]==S[i][j]: return False
		return True
		
	fwd=check(ma, fe)
	rev=check([row[::-1] for row in ma][::-1], fe)
	
	if fwd==rev==False:
		return print(-1)
		
	ans=0	
	fail=1
	for i in range(1,10000):
		ans+=fail*(1-(1/2)**(i-1))*i
		fail*=(1/2)**(i-1)
	print(round(ans,9))
	
	
	
from collections import *
main()