#include <bits/stdc++.h>
using namespace std;

using ld = long double;

int main() {
    int h, w;
    cin >> h >> w;
    vector<vector<char>> s(h, vector<char>(w)), t(h, vector<char>(w));
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            cin >> s[i][j];
        }
    }
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            cin >> t[i][j];
        }
    }
    bool odd = true, even = true;
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (s[i][j] == t[i][j]) {
                odd = false;
            }
            if (s[h - 1 - i][w - 1 - j] == t[i][j]) {
                even = false;
            }
        }
    }
    ld ans = 1.0;
    vector<ld> p(25), mul(25);
    p[1] = mul[1] = 1.0;
    if (odd && even) {
        for (int i = 2; i < 25; i++) {
            ans += mul[i - 1];
            p[i] = p[i - 1] / 2.0;
            mul[i] = mul[i - 1] * p[i];
        }
    } else if (odd && !even) {
        for (int i = 2; i < 25; i++) {
            ans += mul[i - 1];
            p[i] = (i % 2 == 0 ? 1.0 : p[i - 2] / 4.0);
            mul[i] = mul[i - 1] * p[i];
        }
    } else if (!odd && even) {
        for (int i = 2; i < 25; i++) {
            if (i == 2) {
                ans += 1.0;
                p[2] = 0.5;
                mul[2] = 0.5;
            } else {
                ans += mul[i - 1];
                p[i] = (i % 2 == 0 ? p[i - 2] / 4.0 : 1.0);
                mul[i] = mul[i - 1] * p[i];
            }
        }
    } else {
        cout << -1 << endl;
        return 0;
    }
    cout << fixed << setprecision(10) << ans << endl;
}