import sys
input = lambda :sys.stdin.readline()[:-1]
ni = lambda :int(input())
na = lambda :list(map(int,input().split()))
yes = lambda :print("yes");Yes = lambda :print("Yes");YES = lambda : print("YES")
no = lambda :print("no");No = lambda :print("No");NO = lambda : print("NO")
#######################################################################

h,w = na()
s = [list(input()) for i in range(h)]
t = [["#" if x == "." else "." for x in input()] for i in range(h)]


A = (s == t)
B = (s == [x[::-1] for x in t[::-1]])
s = 1
ans = 0
if A or B:
    for i in range(10**6):
        if (i % 2 == 0 and A) or (i % 2 == 1 and B):
            ans += s * (1 - 1/2**i) * (i+1)
            s -= s * (1 - 1/2**i)
        if s < 10**-9:
            break
    print(ans)
else:
    print(-1)