def rot90(A):
    # 時計回りに90度回転
    return list(zip(*(A[::-1])))

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

f = [0, 0]
flag = 1
for i in range(H):
    for j in range(W):
        if S[i][j] == T[i][j] == "#":
            flag = 0
f[0] = flag
T = rot90(rot90(T))
flag = 1
for i in range(H):
    for j in range(W):
        if S[i][j] == T[i][j] == "#":
            flag = 0
f[1] = flag
if sum(f) == 0:
    print(-1)
    exit()
    
ans = 0
p = 1
for i in range(1000):
    if f[i%2]:
        ans += p * (1 - (1/2)**i) * (i + 1)
        p *= (1/2)**i
        
print(ans)