#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ull = unsigned long long;

double hyp(double x, double y) {
	return sqrt(x*x + y*y);
}

struct Cow {
	int x, y, r;

	double dist(double xx, double yy) {
		return max(0.0, hyp(xx-x, yy-y) - r);
	}
};

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout << setprecision(8);

	int n;
	cin >> n;
	vector<Cow> cs(n);
	Cow sumc = {0, 0, 0};
	for(int i = 0; i < n; ++i) {
		int x, y, r;
		cin >> x >> y >> r;
		cs[i] = {x, y, r};
		sumc.x += x;
		sumc.y += y;
		sumc.r += r;
	}
	if(n == 1) {
		cout << 0 << '\n';
		return 0;
	}
	double x = 1.0*sumc.x / n;
	double y = 1.0*sumc.y / n;

	double mmaxd = 1000000000;

	for(double m = 50; m > 0.0000002; m *= 0.99) {
		Cow maxf = cs[0];
		double maxd = cs[0].dist(x, y);
		for(auto c : cs) {
			double d = c.dist(x, y);
			if(d > maxd) {
				maxd = d;
				maxf = c;
			}
		}
		mmaxd = min(maxd, mmaxd);
		x += m*(maxf.x-x)/hyp(maxf.x-x, maxf.y-y);
		y += m*(maxf.y-y)/hyp(maxf.x-x, maxf.y-y);
	}

	cout << mmaxd << '\n';

	return 0;
}