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

int main(void) {
	int h, w;
	cin >> h >> w;

	vector< vector<char> > S(h, vector<char>(w)), T(h, vector<char>(w));
	rep(i, 0, h) {
		rep(j, 0, w) {
			cin >> S[i][j];
		}
	}
	rep(i, 0, h) {
		rep(j, 0, w) {
			cin >> T[i][j];
		}
	}

	bool flag = true, flag2 = true;
	rep(i, 0, h) {
		rep(j, 0, w) {
			if (S[i][j] == T[i][j]) {
				flag = false;
			}
		}
	}
	rep(i, 0, h) {
		rep(j, 0, w) {
			int k = (h - 1) - i;
			int l = (w - 1) - j;

			if (S[k][l] == T[i][j]) {
				flag2 = false;
			}
		}
	}

	cout << fixed << setprecision(10);

	ld ep = 1, q = 1, p = -1;
	if (flag && flag2) {
		rep(i, 1, 21) {
			p = (1 - powl(2, -(i - 1)));
			q *= (1 - p);

			ep += q;
		}
	}
	else if (!flag && flag2) {
		rep(i, 1, 21) {
			if (i % 2 == 0) p = (1 - powl(2, -(i - 1)));
			else p = 0;
			q *= (1 - p);

			ep += q;
		}
	}
	else if (flag && !flag2) {
		rep(i, 1, 21) {
			if (i % 2 != 0) p = (1 - powl(2, -(i - 1)));
			else p = 0;
			q *= (1 - p);

			ep += q;
		}
	}
	else if (!flag && !flag2) {
		ep = -1;
	}

	cout << ep << endl;

	return 0;
}