#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <queue>
#include <vector>
using namespace std;int N, idx;
double R;
const double INF = 1e12;const double eps = 1e-6;
double D[1005][1005];
double H[1005][1005];struct Node {int x, y, z;void read() {scanf("%d %d %d", &x, &y, &z);}
}p[1005];inline int sign(double x) {return x < -eps ? -1 : x > eps ? 1 : 0;
}double dist(int x1, int y1, int x2, int y2) {return sqrt(1.0*(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}double dis[1005];
char vis[1005];struct cmp {bool operator () (const int &a, const int &b) {return sign(dis[a] - dis[b]) > 0;}
};bool Ac(double R) {double sum = 0;memset(vis, 0, sizeof (vis));fill(dis, dis+N, 1e12);dis[0] = 0;for (int i = 0; i < N; ++i) {double Min = INF;int u;for (int i = 0; i < N; ++i) {if (!vis[i] && sign(Min-dis[i])>0) {u = i, Min = dis[i];    }}vis[u] = 1;sum += dis[u];for (int v = 0; v < N; ++v) {if (vis[v]) continue;double ct = H[u][v]-R*D[u][v];if (sign(dis[v]-ct) > 0) {dis[v] = ct;}}}return sign(sum) <= 0;
}double bsearch(double l, double r) {double mid, ret;while (r - l >= eps) {mid = (l + r) / 2.0;if (Ac(mid)) {ret = mid;r = mid - eps;} else {l = mid + eps;    }}return ret;
}int main() {while (scanf("%d", &N), N) {for (int i = 0; i < N; ++i) {p[i].read();}idx = 0;for (int i = 0; i < N; ++i) {for (int j = 0; j < N; ++j) {H[i][j] = abs(p[i].z - p[j].z);D[i][j] = dist(p[i].x, p[i].y, p[j].x, p[j].y);}}printf("%.3f\n", bsearch(0, 1e7));}return 0;
}