#include <bits/stdc++.h>
using namespace std;
template <typename T>
inline bool uax(T &x, T y) {
  return (y > x) ? x = y, true : false;
}
template <typename T>
inline bool uin(T &x, T y) {
  return (y < x) ? x = y, true : false;
}
string to_string(char c) { return "'" + string(1, c) + "'"; }
string to_string(string s) { return '"' + s + '"'; }
string to_string(const char *s) { return to_string((string)s); }
template <typename A>
string to_string(A);
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ": " + to_string(p.second) + ")";
}
template <typename A>
string to_string(A v) {
  bool f = false;
  string r = "{";
  for (auto x : v) {
    if (f) r += ", ";
    r += to_string(x);
    f = true;
  }
  return r += "}";
}
template <typename A>
string to_string(vector<vector<A>> v) {
  string r;
  for (auto x : v) r += "\n" + to_string(x);
  return r;
}
void err(istream_iterator<string>) { cerr << endl; }
template <typename T, typename... Args>
void err(istream_iterator<string> it, T a, Args... args) {
  cerr << *it << " =: " << to_string(a) << "; ";
  err(++it, args...);
}
template <typename T>
void kek(T ans) {
  cout << ans << endl;
  exit(0);
}
int const MOD = 1e9 + 7;
long long const INF = 1e18 + 42;
int32_t main() {
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  int n;
  cin >> n;
  vector<pair<int, int>> a(n);
  for (auto &[x, y] : a) cin >> x >> y;
  {
    int mul = 1;
    if (a[0].second < 0) mul = -1;
    for (auto &[x, y] : a) {
      y *= mul;
      if (y < 0) kek(-1);
    }
  }
  using ld = long double;
  auto can = [&](ld r) {
    ld lo = -INF, hi = INF;
    for (auto &[x, y] : a) {
      ld p = (r + r - y) * y;
      if (p < 1e-9) return false;
      p = sqrt(p);
      uax(lo, x - p);
      uin(hi, x + p);
      if (lo + 1e-9 > hi) return false;
    }
    return true;
  };
  ld lo = 0, hi = 1e16;
  for (int iter = 0; iter < 200; ++iter) {
    ld md = (lo + hi) / 2;
    if (can(md))
      hi = md;
    else
      lo = md;
  }
  cout.precision(9);
  cout << fixed << lo << endl;
  return 0;
}
