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

const int MAXN = 1e5+5;
const ll p = 1e9+7;

int n, g[505][505];

int main() {
	cin >> n;
	int sum = 0;
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j < n; ++j) {
			char x; cin >> x;
			if (x == '.')
				g[i][j] = 0;
			else
				g[i][j] = 1;
			sum += g[i][j];
		}
	}

	if (sum == 0) {
		cout << "-1\n";
		return 0;
	}

	int ct = 0;
	for (int j = 0; j < n; ++j) {
		bool y = 1;
		for (int i = 0; i < n; ++i)
			y &= g[i][j];
		ct += y;
	}

	int mini = 1000;
	//now we just try to make some row all black
	for (int i = 0; i < n; ++i) {
		int s = 0;
		for (int j = 0; j < n; ++j)
			s += g[i][j];
		mini = min(mini, n - s + 1);
		if (s == n)
			mini = 0;
		bool y = 0;
		for (int j = 0; j < n; ++j)
			if (g[j][i] == 1)
				y = 1;
		if (y == 1)
			mini = min(mini, n-s);
	}

	cout << mini + n - ct << endl;
}