/*
 ID: bradyawn
 PROG: contest
 LANG: C++11
 */

#include <iostream>
#include <algorithm>
#include <iomanip>
#include <fstream>
#include <vector>
#include <deque>
#include <string>
#include <cmath>
#include <map>
#include <unordered_map>
#include <utility>
#include <set>
#include <unordered_set>
#include <ctime>
#include <queue>
#include <stack>
#include <bitset>
#include <random>
#include <cstring>
#include <complex>
#include <cassert>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int,int> i2;
typedef pair<ll,ll> ll2;

int n;

int x[100001];
int y[100001];

//1e5 * 30 * 30

const int LOGMAX = 40;
const double EPS = 1e-7;

bool f(double r, double p)
{
    ld ret = 0;
    for (int i = 1; i <= n; i++)
    {
        ld dx = p-x[i];
        ld dy = r-y[i];
        ret = max(ret, dx*dx + dy*dy);
    }
    return ret < (ld)r*r; //farthest squared distance
}

int mx = 0;
double ans = 1e18;
bool ok = false;

int hits = 0;

double calc(double p) //minimum radius needed to work loc p
{
    double lo = 0;
    double hi = (double)mx * mx;
    for (int i = 1; i <= LOGMAX; i++)
    {
        double mid = (lo+hi)/2;
        if (f(mid, p)) {hi = mid; ans = min(ans, mid); }
        else lo = mid;
    }
    return lo;
}

int main()
{
    //ifstream inf("");
    //ofstream outf("");
    cout << setprecision(15);
    ios::sync_with_stdio(0); cin.tie(0);

    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> x[i] >> y[i];
        if (y[i] < 0) hits++;
        mx = max(mx, y[i]);
        mx = max(mx, x[i]);
    }
    if (hits > 0) for (int i = 1; i <= n; i++) {x[i] *= -1; y[i] *= -1;}
    if (hits != n && hits != 0) {cout << -1 << '\n'; return 0;}

    double lo = -2*mx;
    double hi = 2*mx;
    for (int i = 1; i <= LOGMAX; i++)
    {
        double lm = lo + (hi - lo)/3;
        double rm = hi - (hi - lo)/3;
        if (calc(lm) < calc(rm)) hi = rm;
        else lo = lm;
    }

    cout << calc(lo) << '\n';

    return 0;

}