#include <bits/stdc++.h>
using namespace std;
struct ww {
  double x, y;
  inline ww operator+(const ww &A) { return (ww){x + A.x, y + A.y}; }
  inline ww operator-(const ww &A) { return (ww){x - A.x, y - A.y}; }
  inline double operator*(const ww &A) { return x * A.y - y * A.x; }
  inline double operator/(const ww &A) { return x * A.x + y * A.y; }
  inline double com() { return x * x + y * y; }
} a[110];
int i, j, k, n, m, u;
double ma;
inline double dis(ww A, ww B) {
  A = B - A;
  return sqrt(A.com());
}
inline bool get(double a, double b, double c, double d, double e, double f,
                ww &O) {
  double s = b * d - a * e;
  if (!s) return 0;
  O.y = (a * f - c * d) / s;
  O.x = (b * f - c * e) / -s;
  return 1;
}
inline int ju(ww &A, ww &B, ww &C, ww O) {
  ww a[5] = {A, B, C, A, B};
  int i, f1, f2;
  f1 = f2 = 0;
  for (i = 0; i <= 2; i++) {
    double s = (a[i] - O) * (a[i + 1] - O);
    if (abs(s) < (1e-7)) {
      A = a[i], B = a[i + 2], C = a[i + 1];
      return 1;
    }
    if (s < 0) f1 = 1;
    if (s > 0) f2 = 1;
  }
  if (f1 && f2) return 2;
  return 0;
}
inline void work1(ww A, ww B, ww C) {
  ww O;
  if (!get(2 * (B.x - A.x), 2 * (B.y - A.y), A.com() - B.com(), 2 * (C.x - A.x),
           2 * (C.y - A.y), A.com() - C.com(), O))
    return;
  int f = ju(A, B, C, O);
  if (f == 2) return;
  {
    double len = dis(A, O);
    int u;
    for (u = 1; u <= n; u++)
      if (u != i && u != j && u != k && dis(a[u], O) + (1e-7) < len) return;
  }
  if (!f) ma = max(ma, dis(A, O));
  if (f == 1) {
    int u;
    for (u = 1; u <= n; u++)
      if (u != i && u != j && u != k) {
        double s1 = (A - a[u]) / (C - a[u]), s2 = (B - A) / (a[u] - A);
        if (abs(s1) < (1e-7) && abs(s2) < (1e-7)) {
          ma = max(ma, dis(A, C) / 2);
          return;
        }
      }
  }
}
int main() {
  scanf("%d", &n);
  for (i = 1; i <= n; i++) scanf("%lf%lf", &a[i].x, &a[i].y);
  ma = -1;
  for (i = 1; i <= n; i++)
    for (j = i + 1; j <= n; j++)
      for (k = j + 1; k <= n; k++) work1(a[i], a[j], a[k]);
  if (ma < 0)
    printf("-1\n");
  else
    printf("%.12lf\n", ma);
  return 0;
}
