#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int INF = 1e9 + 10;
const ll INFL = 4e18;

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];
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            T[i][j] ^= int('#') ^ int('.');
        }
    }
    auto U = T;
    for (int i = 0; i < H; i++) ranges::reverse(U[i]);
    ranges::reverse(U);

    if (S != U && S != T) {
        cout << -1 << endl;
    } else if (S == T && S == U) {
        cout << "2.641632560655154" << endl;
    } else if (S == T) {
        cout << "3.5317401904617327" << endl;
    } else {
        cout << "3.128936827211877" << endl;
    }
}