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

S = [[1 if S[i][j] == '#' else 0 for j in range(W)] for i in range(H)]
T = [[1 if T[i][j] == '#' else 0 for j in range(W)] for i in range(H)]

a, b = 1, 1
for i in range(H):
    for j in range(W):
        a &= (S[i][j] + T[i][j] == 1)
        b &= (S[H - 1 - i][W - 1 - j] + T[i][j] == 1)

if a == 0 and b == 0:
    exit(print(-1))

a = Decimal(a)
b = Decimal(b)
ans = Decimal(0.0)
sp = Decimal(0.0)
coef = Decimal(1.0)

for k in range(1, 202020):
    if k % 2:
        prob = (Decimal(1.0) - sp) * a * (Decimal(1.0) - coef)
    else:
        prob = (Decimal(1.0) - sp) * b * (Decimal(1.0) - coef)
    ans += prob * Decimal(k)
    sp += prob
    
    coef /= Decimal(2.0)

print(ans)