h,w=map(int,input().split())
s=[input()for i in range(h)]
t=[input()for i in range(h)]
x=1
y=1
for i in range(h):
	for j in range(w):
		if s[i][j]==t[i][j]:x=0
		if s[h-1-i][w-1-j]==t[i][j]:y=0

z=0
ans=0
zan=1
for i in range(1, 101):
	if z==0:
		if x:
			ans+=i*zan*(1-pow(2.0,-i+1))
			zan*=pow(2.0,-i+1)
	else:
		if y:
			ans+=i*zan*(1-pow(2.0,-i+1))	
			zan*=pow(2.0,-i+1)
	z^=1

if ans<0.00001:
	print(-1)
else:
	print(ans)