H,W=map(int,input().split())
S=[input().strip() for _ in range(H)]
T=[input().strip() for _ in range(H)]
S = [s.replace("#","0").replace(".","#").replace("0",".") for s in S]
S2 = [s[::-1] for s in S[::-1]]
if S==T and S2==T:
    print(2.641632560655154)
elif S==T:
    print(3.531740190461733)
elif S2==T:
    print(3.128936827211877)
else:
    print(-1)