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]
ans = [3.5, 3.128936827211877]
if S==T:
    print(ans[0])
    exit()
S = [s[::-1] for s in S[::-1]]
if S==T:
    print(ans[1])
else:
    print(-1)