#include <bits/stdc++.h>
using namespace std;
const int MOD = 998244353;
const int N = 200005;
const double PI = 4 * atan(1);
const long long MAX = 9223372036854775807;
int dx[] = {1, -1, 0, 0, 1, -1, 1, -1};
int dy[] = {0, 0, 1, -1, 1, 1, -1, -1};
long long gcd(long long a, long long b) { return (b == 0 ? a : gcd(b, a % b)); }
long long lcm(long long a, long long b) { return a * (b / gcd(a, b)); }
bool issquare(long long w) { return trunc(sqrt(w)) * trunc(sqrt(w)) == w; }
bool isprime(long long u) {
  for (long long i = 2; i <= (int)sqrt(u); i++) {
    if (u % i == 0) return 0;
  }
  return 1;
}
long long mod(long long to_mod, long long MOD) {
  to_mod %= MOD;
  while (to_mod < 0) to_mod += MOD;
  return to_mod % MOD;
}
long long moduloMultiplication(long long a, long long b, long long mod) {
  long long res = 0;
  a %= mod;
  while (b) {
    if (b & 1) res = (res + a) % mod;
    a = (2 * a) % mod;
    b >>= 1;
  }
  return res;
}
long long power(long long x, long long y) {
  long long res = 1;
  x = x;
  while (y > 0) {
    if (y & 1) res = (res * x);
    y = y >> 1;
    x = (x * x);
  }
  return res;
}
long long _sieve_size;
bitset<15000100> bs;
vector<long long> primes;
void sieve(long long upperbound) {
  _sieve_size = upperbound + 1;
  bs.set();
  bs[0] = bs[1] = 0;
  for (long long i = 2; i <= _sieve_size; i++)
    if (bs[i]) {
      for (long long j = i * i; j <= _sieve_size; j += i) bs[j] = 0;
      primes.push_back(i);
    }
}
long double n, m, x, y, t, k, z, w, l, r, ans, a;
vector<pair<long double, long double> > v;
bool pos = false, neg = false;
bool check(long double r) {
  long double trollleft = -1e17;
  long double trollright = 1e17;
  for (int i = 0; i < n; i++) {
    long double easy = sqrt(r * r - (r - v[i].second) * (r - v[i].second));
    long double le = v[i].first - easy;
    long double ri = v[i].first + easy;
    trollleft = max(trollleft, le);
    trollright = min(trollright, ri);
    if (trollright < trollleft) return false;
  }
  return true;
}
int main() {
  cin >> n;
  l = 1e9;
  r = -1e9;
  long double lef = 0, righ = 1e12;
  for (int i = 0; i < n; i++) {
    cin >> x >> y;
    l = min(l, x / 100.0);
    r = max(r, x / 100.0);
    if (y < 0)
      neg = true;
    else
      pos = true;
    lef = max(lef, abs(y) / 200.0);
    v.push_back(make_pair(x / 100.0, abs(y) / 100.0));
  }
  if (n == 1) {
    printf("%.20Lf", v[0].second * 50.0);
    return 0;
  }
  if (neg && pos) {
    cout << -1;
    return 0;
  }
  while (abs(lef - righ) > (1e-7) / 2) {
    long double mid = (lef + righ) / 2;
    if (check(mid)) {
      righ = mid;
    } else {
      lef = mid;
    }
  }
  long double mid = (lef + righ) / 2;
  if (mid != righ) {
    if (check(mid)) {
      righ = mid;
    } else {
      lef = mid;
    }
  }
  printf("%.8Lf", (lef + righ) * 50.0);
  return 0;
}
