#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define ALL(v) v.begin(),v.end()
#define dbg(x) cerr << #x << ": " << (x) << endl;
template<class F, class S>
ostream& operator<<(ostream& os, pair<F,S>& p) {
    os << '(' << p.first << ',' << p.second << ')';
    return os;
}
template<class Iter>
void print(Iter beg, Iter end) {
    for (Iter itr = beg; itr != end; ++itr) {
        cerr << *itr << ' ';
    }
    cerr << '\n';
}
int h,w;
vector<string> s,t;

int main() {
    cin >> h >> w;
    s.resize(h); t.resize(h);
    for (int i = 0; i < h; ++i) cin >> s[i];
    for (int i = 0; i < h; ++i) cin >> t[i];

    for (int i = 0; i < h; ++i) for (int j = 0; j < w; ++j) s[i][j] = (s[i][j]=='#' ? '.' : '#');

    bool f1 = (s == t);
    reverse(ALL(s));
    for (int i = 0; i < h; ++i) reverse(ALL(s[i]));
    bool f2 = (s == t);

    if (!f1 && !f2) {
        cout << -1 << '\n';
        return 0;
    }
    double base = 1;
    double ans = 0;
    for (int t = 1; t < 60; ++t) {
        double p = 1.0 / (1LL << (t-1));
        if (t % 2 == 1 && f1 || t % 2 == 0 && f2) {
            // cerr << t << " " << base * (1-p) << '\n';
            ans += t * base * (1-p);
            base *= p;
        }
    }

    cout << fixed << setprecision(20) << ans << '\n';
}