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;
typedef pair<long long, long long> ll;
typedef vector<long long> vl;
typedef vector<ll> vll;
typedef vector<vl> vvl;
template <typename T>
ostream &operator<<(ostream &o, vector<T> v) {
  if (v.size() > 0) o << v[0];
  for (unsigned i = 1; i < v.size(); i++) o << " " << v[i];
  return o << "\n";
}
template <typename U, typename V>
ostream &operator<<(ostream &o, pair<U, V> p) {
  return o << "(" << p.first << ", " << p.second << ") ";
}
template <typename T>
istream &operator>>(istream &in, vector<T> &v) {
  for (unsigned i = 0; i < v.size(); i++) in >> v[i];
  return in;
}
template <typename T>
istream &operator>>(istream &in, pair<T, T> &p) {
  in >> p.first;
  in >> p.second;
  return in;
}
struct pt {
  long double x, y;
};
vector<vector<long double>> sdist(110, vector<long double>(110));
vvl dist(110, vl(110));
long long n;
long double fun(long double a, long double b, long double c) {
  a = sqrt(a);
  b = sqrt(b);
  c = sqrt(c);
  return a * b * c /
         sqrt((a + b + c) * (a + b - c) * (-a + b + c) * (a - b + c));
}
vector<pt> P(110);
pt circum_center(pt a, pt b, pt c) {
  long double x1 = b.x - a.x;
  long double y1 = b.y - a.y;
  long double x2 = c.x - a.x;
  long double y2 = c.y - a.y;
  long double x = (y2 * (x1 * x1 + y1 * y1) - y1 * (x2 * x2 + y2 * y2)) / 2.0 /
                  (x1 * y2 - x2 * y1);
  long double y = -(x2 * (x1 * x1 + y1 * y1) - x1 * (x2 * x2 + y2 * y2)) / 2.0 /
                  (x1 * y2 - x2 * y1);
  pt ans = {a.x + x, a.y + y};
  return ans;
}
bool check(pt p, long double d) {
  long double x2 = p.x, y2 = p.y;
  for (long long i = (0); i < (long long)n; i++) {
    long double dx = P[i].x - x2;
    long double dy = P[i].y - y2;
    if ((dx * dx + dy * dy) / d < 1.0 - 1e-8) return false;
  }
  return true;
}
int main() {
  cout.precision(20);
  cin >> n;
  for (long long i = (0); i < (long long)n; i++) cin >> P[i].x >> P[i].y;
  long double ans = -1.0;
  for (long long i = (0); i < (long long)n; i++)
    for (long long j = (0); j < (long long)n; j++) {
      long long dx = P[i].x - P[j].x, dy = P[i].y - P[j].y;
      dist[i][j] = dx * dx + dy * dy;
      sdist[i][j] = sqrt(dist[i][j]);
    }
  for (long long(k) = 0; (k) < (n); (k)++)
    for (long long(j) = 0; (j) < (k); (j)++)
      for (long long(i) = 0; (i) < (j); (i)++) {
        long long d1 = dist[i][j], d2 = dist[j][k], d3 = dist[k][i];
        if (d1 + d2 > d3 and d2 + d3 > d1 and d3 + d1 > d2) {
          long double temp = fun(d1, d2, d3);
          pt O = circum_center(P[i], P[j], P[k]);
          if (check(O, temp * temp)) ans = max(ans, temp);
        }
      }
  for (long long i = (0); i < (long long)n; i++)
    for (long long j = (0); j < (long long)i; j++) {
      bool found = false;
      for (long long(k) = 0; (k) < (n); (k)++)
        for (long long(l) = 0; (l) < (k); (l)++) {
          if (!found and dist[i][j] == dist[k][l] and
              dist[i][k] == dist[j][l] and dist[i][l] == dist[j][k] and
              dist[i][j] > dist[i][k] and dist[i][j] > dist[i][l]) {
            found = true;
            long double temp = sdist[i][j] / 2.0;
            pt O = {(P[i].x + P[j].x) / 2.0, (P[i].y + P[j].y) / 2.0};
            if (check(O, temp * temp)) ans = max(ans, temp);
          }
        }
    }
  if (ans < -0.5)
    cout << "-1"
         << "\n";
  else
    cout << ans << "\n";
  return 0;
}