#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const long long int inf = 2e18;
const long double eps = 1e-9;
const int NN = 1e5 + 2;
void solve() {
  cerr << fixed << setprecision(10);
  int i = 0, j = 0, k = 0, n = 0, m = 0;
  cin >> n;
  bool b1 = 0, b2 = 0;
  vector<long long int> x(n), y(n);
  for (i = 0; i < (n); i++) {
    cin >> x[i] >> y[i];
    if (y[i] < 0) b1 = 1;
    if (y[i] > 0) b2 = 1;
    ;
  };
  if (b1 && b2) {
    cout << -1 << '\n';
    return;
  }
  if (b1) {
    for (i = 0; i < (n); i++) {
      y[i] *= -1;
    }
  }
  long double lo = eps, hi = inf / 4, r;
  for (i = 0; i < 200; i++) {
    r = (hi + lo) / 2;
    ;
    long double xc = -inf;
    bool is = 1;
    long double xc_l = inf;
    for (j = 0; j < n; j++) {
      long double diff = y[j] - 2 * r;
      if (diff > 0) {
        is = 0;
        break;
      }
      diff = 2 * y[j] * r - y[j] * y[j];
      if (diff < 0) {
        is = 0;
        break;
      }
      long double d = sqrt(diff) < 0 ? 0 : sqrt(diff);
      xc = max(xc, x[j] - d);
      xc_l = min(xc_l, d + x[j]);
    };
    if (!is) {
      lo = r + eps;
      continue;
    }
    if (xc_l >= xc) {
      hi = r;
    } else
      lo = r + eps;
  }
  cout << fixed << setprecision(15) << hi << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int T = 1, tc;
  for (tc = 1; tc <= T; tc++) {
    solve();
  }
  return 0;
}
