#include <bits/stdc++.h>
#pragma GCC optimize("O3")
const double pi = acos(-1);
const int MOD = 1e9 + 7;
const int INF = 1e9 + 7;
const int MAXN = 1e3 + 5;
const double eps = 1e-6;
using namespace std;
int X[MAXN], Y[MAXN];
double ans = 0;
int dp[MAXN][MAXN], n = 0;
double cross(int i, int j, int k) {
  return (X[j] - X[i]) * (X[k] - X[i]) + (Y[j] - Y[i]) * (Y[k] - Y[i]);
}
void f(double x, double y, double mi) {
  for (int i = 0; i < n; i++)
    if (hypot(X[i] - x, Y[i] - y) + eps < mi) return;
  ans = max(ans, mi);
}
int main() {
  scanf("%d", &(n));
  for (int i = 0; i < n; i++) scanf("%d %d", X + i, Y + i);
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++)
      dp[i][j] = (X[i] - X[j]) * (X[i] - X[j]) + (Y[i] - Y[j]) * (Y[i] - Y[j]);
  for (int i = 0; i < n; i++)
    for (int j = i + 1; j < n; j++)
      for (int k = j + 1; k < n; k++)
        if (cross(i, j, k) > 0 && cross(j, i, k) > 0 && cross(k, i, j) > 0) {
          double a1 = -2 * (X[j] - X[i]);
          double b1 = -2 * (Y[j] - Y[i]);
          double c1 = X[i] * X[i] - X[j] * X[j] + Y[i] * Y[i] - Y[j] * Y[j];
          double a2 = -2 * (X[k] - X[i]);
          double b2 = -2 * (Y[k] - Y[i]);
          double c2 = X[i] * X[i] - X[k] * X[k] + Y[i] * Y[i] - Y[k] * Y[k];
          if (X[i] == X[j]) swap(a1, a2), swap(b1, b2), swap(c1, c2);
          b2 -= b1 * a2 / a1;
          c2 -= c1 * a2 / a1;
          double b = c2 / b2;
          c1 -= b1 * b;
          double a = c1 / a1;
          f(a, b, hypot(X[i] - a, Y[i] - b));
        }
  for (int i = 0; i < n; i++)
    for (int j = 0; j < n; j++) {
      if (i == j) continue;
      for (int k = 0; k < n; k++) {
        if (i == k || k == j) continue;
        for (int l = 0; l < n; l++) {
          if (i == l || l == j || k == l) continue;
          if (!(dp[i][j] == dp[k][l] && dp[i][k] == dp[j][l] &&
                dp[i][j] + dp[j][k] == dp[i][k]))
            continue;
          f(0.5 * (X[i] + X[k]), 0.5 * (Y[i] + Y[k]), sqrt(dp[i][k]) / 2.);
        }
      }
    }
  if (ans < eps) return !printf("%d\n", (-1));
  printf("%.20f\n", ans);
  return 0;
}
