using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    static string[] SList(long n) => Enumerable.Repeat(0, (int)n).Select(_ => ReadLine()).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var c = NList;
        var (h, w) = (c[0], c[1]);
        var s = SList(h);
        var t = SList(h);
        var first = Connect(s, t);
        var second = Connect(Reverse(s), t);
        var fail = 1.0;
        var mul = 1.0;
        var ans = 0.0;
        for (var i = 1; i < 100; ++i)
        {
            if ((i % 2 == 1 && first) || (i % 2 == 0 && second))
            {
                ans += i * mul * (1 - fail);
                mul *= fail;
            }
            fail /= 2;
        }
        WriteLine(ans == 0 ? -1 : ans);
    }
    static string[] Reverse(string[] s)
    {
        var ans = new string[s.Length];
        for (var i = 0; i < s.Length; ++i) ans[i] = string.Concat(s[s.Length - i - 1].Reverse());
        return ans;
    }
    static bool Connect(string[] s, string[] t)
    {
        for (var i = 0; i < s.Length; ++i) for (var j = 0; j < s[0].Length; ++j) if (s[i][j] == t[i][j]) return false;
        return true;
    }
}