#include <bits/stdc++.h>
using namespace std;
const int N = 1e5 + 5;
const long double INF = 1e16;
const long double eps = 1e-9;
int n;
pair<long double, long double> p[N];
bool can(long double R) {
  long double l = -INF, r = INF;
  for (int i = 1; i <= n; i++) {
    long double delta = 8 * R * p[i].second - 4 * p[i].second * p[i].second;
    if (delta < -eps) return false;
    long double D = (delta < 0 ? 0 : sqrt(delta)) / 2.0;
    l = max(l, p[i].first - D);
    r = min(r, p[i].first + D);
  }
  return !(l > r + eps);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cin >> n;
  bool pos = false, neg = false;
  for (int i = 1; i <= n; i++) {
    cin >> p[i].first >> p[i].second;
    if (p[i].second > 0) {
      pos = true;
    } else {
      neg = true;
    }
  }
  if (pos == neg) {
    cout << -1 << '\n';
    return 0;
  }
  if (neg) {
    for (int i = 1; i <= n; i++) p[i].second = -p[i].second;
  }
  long double l = 0, r = INF;
  if (can(1)) {
    r = 1;
  } else {
    l = 1;
  }
  long double ans = INF;
  for (int i = 0; i < 150; i++) {
    long double mid = (l + r) / 2.0;
    if (can(mid)) {
      r = mid;
      ans = mid;
    } else {
      l = mid;
    }
  }
  cout << fixed << setprecision(12) << ans << '\n';
  return 0;
}
