Problem: Luyi has n circles on the plane. The i-th circle is centered at (xi, yi). At the time zero circles start to grow simultaneously. In other words, the radius of each circle at time t (t > 0) is equal to t. The circles are drawn as black discs on an infinite white plane. So at each moment the plane consists of several black and white regions. Note that the circles may overlap while growing.

<image>

We define a hole as a closed, connected white region. For instance, the figure contains two holes shown by red border. During growing some holes may be created and it is easy to see that each created hole will disappear eventually. Luyi asks you to find moment of time such that the last hole disappears. In other words, you should find the first moment such that no hole can be seen after that.

Input

The first line of the input contains integer n (1 ≤ n ≤ 100). Each of the next n lines contains two integers xi and yi ( - 104 ≤ xi, yi ≤ 104), indicating the location of i-th circle.

It's guaranteed that no two circles are centered at the same point.

Output

Print the moment where the last hole disappears. If there exists no moment in which we can find holes print -1.

The answer will be considered correct if the absolute or relative error does not exceed 10 - 4.

Examples

Input

3
0 0
1 1
2 2


Output

-1


Input

4
0 0
0 2
2 2
2 0


Output

1.414214


Input

4
0 1
0 -1
-2 0
4 0


Output

2.125000

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
struct Point {
  int x, y;
  Point(int a, int b) { x = a, y = b; }
  Point() {}
  Point operator+(const Point &p) const { return Point(x + p.x, y + p.y); }
  Point operator-(const Point &p) const { return Point(x - p.x, y - p.y); }
  int operator*(const Point &p) const { return x * p.x + y * p.y; }
  int operator^(const Point &p) const { return x * p.y - y * p.x; }
  bool operator==(const Point &p) const {
    return make_pair(x, y) == make_pair(p.x, p.y);
  }
};
double len(Point p) { return sqrt(p * p); }
int sign(int x) {
  if (x < 0) return -1;
  if (x == 0) return 0;
  return 1;
}
bool inside(Point A, Point B, Point C, Point q) {
  int s1 = sign((B - A) ^ (q - A)), s2 = sign((C - B) ^ (q - B)),
      s3 = sign((A - C) ^ (q - C));
  return (s1 * s2 >= 0 && s2 * s3 >= 0 && s3 * s1 >= 0);
}
int Type(Point A, Point B, Point C) {
  Point AB = B - A, AC = C - A, BC = C - B, BA = A - B, CA = A - C, CB = B - C;
  int dot = AB * AC;
  if (dot < 0) return -1;
  if (dot == 0) return 2;
  dot = BA * BC;
  if (dot < 0) return -1;
  if (dot == 0) return 3;
  dot = CA * CB;
  if (dot < 0) return -1;
  if (dot == 0) return 4;
  return 1;
}
double Acos(double x) {
  if (x > 1.0) x = 1.0;
  if (x < -1.0) x = -1.0;
  return acos(x);
}
double peri_rad(Point A, Point B, Point C) {
  Point AB = B - A, AC = C - A, BC = C - B;
  double BAC = Acos((AB * AC) / len(AB) / len(AC));
  return 0.5 * len(BC) / sin(BAC);
}
pair<double, double> pori_britto(Point p1, Point p2, Point p3) {
  double Bx = p2.x - p1.x, By = p2.y - p1.y;
  double Cx = p3.x - p1.x, Cy = p3.y - p1.y, D = 2 * (Bx * Cy - By * Cx);
  double cx = (Cy * (Bx * Bx + By * By) - By * (Cx * Cx + Cy * Cy)) / D + p1.x;
  double cy = (Bx * (Cx * Cx + Cy * Cy) - Cx * (Bx * Bx + By * By)) / D + p1.y;
  return make_pair(cx, cy);
}
double dist(pair<double, double> cen, Point p) {
  double dx = cen.first - p.x, dy = cen.second - p.y;
  return sqrt(dx * dx + dy * dy);
}
const int N = 105;
vector<int> perp[N][N];
int main() {
  int n;
  cin >> n;
  vector<Point> P(n);
  for (int i = 0; i < n; i++) cin >> P[i].x >> P[i].y;
  bool found = false;
  double ans = 0;
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      for (int k = j + 1; k < n; k++) {
        if (((P[j] - P[i]) ^ (P[k] - P[i])) == 0) continue;
        bool bad = false;
        pair<double, double> cen = pori_britto(P[i], P[j], P[k]);
        double rad = peri_rad(P[i], P[j], P[k]);
        for (int l = 0; l < n; l++) {
          if (l == i or l == j or l == k) continue;
          double D = dist(cen, P[l]);
          if (D + eps < rad) {
            bad = true;
            break;
          }
        }
        if (bad) continue;
        int typ = Type(P[i], P[j], P[k]);
        if (typ == -1) continue;
        if (typ == 1) {
          found = true;
          ans = max(ans, rad);
        } else if (typ == 2) {
          perp[j][k].push_back(i);
        } else if (typ == 3) {
          perp[i][k].push_back(j);
        } else if (typ == 4) {
          perp[i][j].push_back(k);
        }
      }
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = i + 1; j < n; j++) {
      int up = 0, down = 0;
      for (int idx : perp[i][j]) {
        if (((P[j] - P[i]) ^ (P[idx] - P[i])) > 0) up = true;
        if (((P[j] - P[i]) ^ (P[idx] - P[i])) < 0) down = true;
      }
      if (up && down) {
        found = true;
        ans = max(ans, 0.5 * len(P[i] - P[j]));
      }
    }
  }
  if (found)
    cout << setprecision(12) << fixed << ans << endl;
  else
    cout << "-1" << endl;
}