#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int h, w;
  cin >> h >> w;
  vector<string> s(h), t(h);
  for (int i = 0; i < h; ++i) cin >> s[i];
  for (int i = 0; i < h; ++i) cin >> t[i];
  int flag[2] = {1, 1};
  for (int _t = 0; _t < 2; ++_t)
  {
    reverse(s.begin(), s.end());
    int tmp = 1;
    for (int i = 0; i < h; ++i)
    {
      for (int j = 0; j < w; ++j)
      {
        if (s[i][j] == t[i][j])
        {
          tmp = 0;
          i = h, j = w;
        }
      }
    }
    flag[_t] = tmp;
  }
  if (flag[0] == 0 && flag[1] == 0)
  {
    cout << -1 << endl;
    return 0;
  }
  double ans = 0, v = 1, now = 1;
  for (int i = 1; i < 10000; ++i)
  {
    if (flag[i % 2])
    {
      ans += now * i * (1 - v);
      now *= v;
    }
    v /= 2.0;
  }
  printf("%.10f\n", ans);
}