h,w=map(int,input().split())
s=[list(input()) for i in range(h)]
t=[list(input()) for i in range(h)]
f=1
for i in range(h):
  for j in range(w):
    f&=s[i][j]!=t[i][j]
if f:
  p=0
  o=0
  x=1
  for i in range(1,200,2):
    o,x=x*(1-2**(-(i-1))),x*(2**(-(i-1)))
    p+=i*o
  print(p)
  exit()
ns=[["."]*w for i in range(h)]
for i in range(h):
  for j in range(w):
    ns[i][j]=s[~i][~j]
s=ns
f=1
for i in range(h):
  for j in range(w):
    f&=s[i][j]!=t[i][j]
if f:
  p=0
  o=0
  x=1
  for i in range(2,200,2):
    o,x=x*(1-2**(-(i-1))),x*(2**(-(i-1)))
    p+=i*o
  print(p)
  exit()
print(-1)