#include <iostream>
#include <string>
#include <cstring>
#include <cstdio>
#include <cmath>
#define inf d[0][0]
using namespace std;
int n, x[200], y[200];
double d[200][200];
double dis(int i, int j) {
	return sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]));
}
int fa[200];
int get(int x) {
	if (fa[x] == x) return x;
	return fa[x] = get(fa[x]);
}
void connect(int x, int y) {
	int fa_x = get(x);
	int fa_y = get(y);
	if (fa_x != fa_y) {
		fa[x] = y;
	}
}
void init() {
	cin >> n;
	memset(d, 127, sizeof(d));
	for (int i = 1; i <= n; i++) {
		cin >> x[i] >> y[i];
		fa[i] = i;
	}
	for (int i = 1; i <= n; i++) {
		string s;
		cin >> s;
		for (int j = 1; j <= n; j++) {
			if (s[j - 1] == '0') {
				d[i][j] = inf;
			} else {
				d[j][i] = dis(i, j);
				connect(i, j);
			}
		}
		d[i][i] = 0;
	}
}
void Floyd() {
	for (int k = 1; k <= n; k++) {
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= n; j++) {
				if (get(i) == get(j) && get(i) == get(k)) {
					if (d[i][k] != inf && d[k][j] != inf) {
						d[i][j] = min(d[i][j], d[i][k] + d[k][j]);
					}
				}
			}
		}
	}
}
double MAX[200];
void find_max() {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (get(i) == get(j) && d[i][j] != inf) {
				MAX[i] = max(MAX[i], d[i][j]);
			}
		}
	}
}
double search() {
	double ans = inf;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (get(i) != get(j)) {
				ans = min(ans, MAX[i] + MAX[j] + dis(i, j));
			}
		}
	}
	for (int i = 1; i <= n; i++) {
		ans = max(ans, MAX[i]);
	}
	return ans;
}
int main() {
	init();
	Floyd();
	find_max();
	printf("%.6f", search());
	return 0;
}