#include <bits/stdc++.h>
using namespace std;
pair<double, double> a[100001];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int n;
  cin >> n;
  bool pl = false, mi = false;
  for (int i = 0; i < n; i++) {
    cin >> a[i].first >> a[i].second;
    if (a[i].second < 0) {
      mi = true;
      a[i].second = -a[i].second;
    } else {
      pl = true;
    }
  }
  if (mi && pl) {
    cout << -1 << '\n';
    return 0;
  }
  double l = 0;
  double r = 1e15;
  int time = 75;
  while (time--) {
    double mid = (l + r) / 2.0;
    bool f = false;
    double x = -1e18, y = 1e18;
    for (int i = 0; i < n; i++) {
      double b = (long long)2.0 * (a[i].first);
      double c = (a[i].first) * (a[i].first) + (a[i].second) * (a[i].second) -
                 (long long)2.0 * (a[i].second) * mid;
      double D = b * b - 4.0 * c;
      if (D < 0) {
        f = true;
        break;
      }
      double nx = (b - sqrt(D)) / 2.0;
      double ny = (b + sqrt(D)) / 2.0;
      if (x > ny || nx > y) {
        f = true;
        break;
      }
      x = max(x, nx);
      y = min(y, ny);
    }
    if (f) {
      l = mid;
    } else
      r = mid;
  }
  cout << fixed;
  cout.precision(15);
  cout << l << '\n';
}
