#include<bits/stdc++.h>
#define int long long
#define endl "\n"
#define write ios::sync_with_stdio(0);
#define by cin.tie(0);
#define ikun_xiaoheizi cout.tie(0);
#define INF 0x3f3f3f3f3f
using namespace std;
double g[155][155], d[155][155], fm[155], x[155], y[155];
int n;
char s[155];

void Floyd() {
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			d[i][j] = g[i][j];
		}
	}
	for (int k = 1; k <= n; k++) {
		for (int i = 1; i <= n; i++) {
			for (int j = 1; j <= n; j++) {
				if (d[i][k] != INF && d[k][j] != INF && d[i][k] + d[k][j] < d[i][j]) {
					d[i][j] = d[i][k] + d[k][j];
				}
			}
		}
	}
}

signed main() {
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> x[i] >> y[i];
	}
	for (int i = 1; i <= n; i++) {
		scanf("%s", s + 1);
		for (int j = 1; j <= n; j++) {
			if (s[j] == '1') {
				g[i][j] = sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j]));
			} else if (i != j) {
				g[i][j] = INF;
			}
		}
	}
	Floyd();
	double mx = 0;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (d[i][j] < INF) {
				fm[i] = max(fm[i], d[i][j]);
			}
		}
		mx = max(mx, fm[i]);
	}
	double ans = INF;
	for (int i = 1; i <= n; i++) {
		for (int j = 1; j <= n; j++) {
			if (d[i][j] >= INF) {
				double t = sqrt((x[i] - x[j]) * (x[i] - x[j]) + (y[i] - y[j]) * (y[i] - y[j])) + fm[i] + fm[j];
				ans = min(ans, t);
			}
		}
	}
	printf("%.6lf\n", max(ans, mx));
	return 0;
}