#include <bits/stdc++.h>
using namespace std;
bool f = 0;
const double eps = 1e-8;
int n;
struct point {
  double x, y;
} p[100010];
inline int rd() {
  int x = 0;
  bool f = 0;
  char c = getchar();
  while (!isdigit(c)) {
    if (c == '-') f = 1;
    c = getchar();
  }
  while (isdigit(c)) {
    x = (x << 1) + (x << 3) + (c ^ 48);
    c = getchar();
  }
  return f ? -x : x;
}
inline bool valid(double x) {
  double l = -(double)1e18, r = (double)1e18, dlt;
  for (register int i = 1; i <= n; ++i) {
    if (p[i].y > x + x) return 0;
    dlt = sqrt(p[i].y * (2 * x - p[i].y));
    l = max(l, p[i].x - dlt);
    r = min(r, p[i].x + dlt);
  }
  return (r - l + eps >= 0.0);
}
int main() {
  n = rd();
  for (register int i = 1; i <= n; ++i) {
    p[i].x = (double)rd();
    p[i].y = (double)rd();
    if (p[i].y < 0.0) f = 1;
  }
  if (f == 1)
    for (register int i = 1; i <= n; ++i) {
      p[i].y = -p[i].y;
      if (p[i].y < 0.0) {
        puts("-1");
        return 0;
      }
    }
  int t = 0;
  register double l = 0.0, r = (double)1e18, mid;
  while (t <= 300) {
    mid = (l + r) / 2.0;
    ++t;
    valid(mid) ? r = mid : l = mid;
  }
  printf("%.10lf", l);
  return 0;
}
