H, W = map(int, input().split())
S = [input() for _ in range(H)]
T = [input() for _ in range(H)]

def flip(S):
    res = [''] * H
    for i in range(H):
        for j in range(W):
            if S[i][j] == '.':
                res[i] += '#'
            else:
                res[i] += '.'
    return res

def rotate(S):
    S.reverse()
    S = [s[::-1] for s in S]
    return S

S = flip(S)

if S != T and rotate(S) != T:
    print(-1)
    exit()

ans = 0.0
M = 20

# i回目の成功確率
p = [0.0] * M

# 成功するまでにちょうどn回かかる確率
q = [0.0] * M

for i in range(1, M):
    if S == T:
        p[i] = 1.0 - 2.0**(1-i)
        q[i] = p[i]
        for j in range(1, i):
            q[i] *= 1.0 - p[j]
        ans += i * q[i]
    S = rotate(S)
print(ans)