import math
import sys


def input():
    return sys.stdin.readline().strip()


def main():
    a, b = map(int, input().split())

    def r(s):
        k = []
        for c in s:
            if c == ".":
                k.append("#")
            else:
                k.append(".")
        return "".join(k)

    z = [input() for _ in range(a)]
    k = [r(input()) for _ in range(a)]

    ok = z == k
    re = z == k[::-1]

    if not ok and not re:
        print("-1")
        return

    rem = 0
    pr = 1

    for i in range(100):
        if (i % 2 == 0 and ok) or (i % 2 == 1 and re):
            rem += pr * ((i+1) * (1 - 0.5 ** i))
            pr *= 0.5 ** i

    print(rem)


if __name__ == "__main__":
    main()