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

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];
            if (s[i][j] == t[i][j]) {
                cout << -1 << endl;
                return 0;
            }
        }
    }
    cout << "3.5317401904617327" << endl;
}