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

ok = []
for i in range(2):
    flg = True
    for i in range(h):
        for j in range(w):
            if S[i][j] == T[i][j]:
                flg = False
                break
        if not flg:
            break
    ok.append(flg)
    S = [row[::-1] for row in S[::-1]]

if not ok[0] and not ok[1]:
    print(-1)
    exit()
ans = 0
p = 1
p2 = 1
for i in range(10000):
    if i % 2 == 0 and ok[i & 1]:
        ans += p2 * (1 - p) * (i + 1)
        p2 *= p
    elif i % 2 == 1 and ok[i & 1]:
        ans += p2 * (1 - p) * (i + 1)
        p2 *= p
    p /= 2
print(ans)