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

#define rep(i, n) for( int i = 0; i < n; i++ )
using ll = long long;

int main() {
	int H, W;
	cin >> H >> W;
	vector<string> s(H), t(H); 
	rep(i, H) cin >> s[i];
	rep(i, H) cin >> t[i];

	int f = 0;
	rep(i, H) rep(j, W) {
		if(s[i][j] == t[i][j]) f = 1;
	}
	int g = 0;
	rep(i, H) rep(j, W) {
		int ii = H - 1 - i;
		int jj = W - 1 - j;
		if(s[ii][jj] == t[i][j]) g = 1;
	}
	if(f && g) cout << -1 << endl;
	else {
		double ans = 0;
		if(g) {
			rep(i, 20) {
				int n = i + 1;
				int dn = n / 2;
				ans += exp2(-(dn * dn - dn));
			}
		}
		else if(f) {
			rep(i, 20) {
				int n = i + 1;
				int dn = (n - 1) / 2;
				ans += exp2(-(dn * dn));
			}
		}
		else {
			rep(i, 20) {
				int n = i + 1;
				ans += exp2(-((n - 2) * (n - 1) / 2));
			}
		}
		cout << fixed << setprecision(12) << ans << endl;
	}
}