#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

const long double EPS = 1e-8, LD1 = 1;
void solve() {
  ll h, w;
  cin >> h >> w;
  vector<string> s(h), t(h);
  rep(i, h) cin >> s[i];
  rep(i, h) cin >> t[i];
  vector<ll> ok(2, 1);
  rep(k, 2) rep(si, h) rep(sj, w) {
    ll ti = si, tj = sj;
    if (k)
      ti = h - si - 1, tj = w - sj - 1;
    ok[k] &= s[si][sj] != t[ti][tj];
  }
  if (!ok[0] && !ok[1]) {
    cout << "-1\n";
    return;
  }
  long double ans = 0, p = 1, pow2 = 1;
  rep(i, 100) {
    if (ok[i % 2]) {
      long double cp = LD1 - LD1 / pow2;
      long double now = (long double)(i + 1) * p * cp;
      if (i > 10 && now < EPS) {
        cout << fixed << setprecision(16) << ans << '\n';
        return;
      }
      ans += now;
      p *= LD1 - cp;
    }
    pow2 *= 2;
  }
}

int main() {
  std::cin.tie(nullptr);
  std::ios_base::sync_with_stdio(false);
  int T = 1;
  for (int t = 0; t < T; t++) {
    solve();
  }
  return 0;
}