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

first, second = False, False
R = [t[:] for t in T[:]]
for i in range(H):
    for j in range(W):
        if R[i][j] == "#":
            R[i][j] = "."
        else:
            R[i][j] = "#"
if S == R:
    first = True
R = [[""]*W for _ in range(H)]
for i in range(H):
    for j in range(W):
        if T[i][j] == "#":
            s = "."
        else:
            s = "#"
        R[-(i+1)][-(j+1)] = s
if S == R:
    second = True

if not first and not second:
    exit(print(-1))

ans = 0
P = 1
for i in range(100):
    p = P*((2**i-1)/2**i)
    if i%2 == 0 and first:
        ans += (i+1)*p
        P -= p
    elif i%2 == 1 and second:
        ans += (i+1)*p
        P -= p

print(ans)