H, W = map(int, input().split())
S = []
for _ in range(H):
    S.append(input())
T = []
Trev = []
for _ in range(H):
    s = input()
    s = s.replace(".", "@")
    s = s.replace("#", ".")
    s = s.replace("@", "#")
    Trev.append(s[::-1])
    T.append(s)
Trev = Trev[::-1]
if S == T and S == Trev:
    pro = 1
    n = 1
    count = 1
    ans = 0
    while (10**10) > n:
        sub = 1 - 1 / n
        ans += sub * pro * count
        pro -= sub * pro
        n *= 2
        count += 1
    print(ans)
elif S == T:
    pro = 1
    n = 1
    count = 1
    ans = 0
    while (10**10) > n:
        if count % 2 == 1:
            sub = 1 - 1 / n
            ans += sub * pro * count
            pro -= sub * pro
        n *= 2
        count += 1
    print(ans)
elif S == Trev:
    pro = 1
    n = 1
    count = 1
    ans = 0
    while (10**10) > n:
        if count % 2 == 0:
            sub = 1 - 1 / n
            ans += sub * pro * count
            pro -= sub * pro
        n *= 2
        count += 1
    print(ans)
else:
    print(-1)