增量法的最小包围圈算法，不会……
#include <cstdio>
#include <cstring>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
const double EPS = 1e-10;
inline int sgn(double x) { return (x > EPS) - (x < -EPS);}
struct Point {
double x, y;
Point() {}
Point(double x, double y) : x(x),y(y) {}
bool operator < (Point a) const { return sgn(x - a.x) < 0 || sgn(x - a.x) == 0 && sgn(y - a.y) < 0;}
bool operator == (Point a) const { return sgn(x - a.x) == 0 && sgn(y - a.y) == 0;}
Point operator + (Point a) const { return Point(x + a.x, y + a.y);}
Point operator - (Point a) const { return Point(x - a.x, y - a.y);}
Point operator * (double p) const { return Point(x * p, y * p);}
Point operator / (double p) const { return Point(x / p, y / p);}
} ;
typedef Point Vec;
inline double crossDet(Vec a, Vec b) { return a.x * b.y - a.y * b.x;}
inline double crossDet(Point o, Point a, Point b) { return crossDet(a - o, b - o);}
inline double dotDet(Vec a, Vec b) { return a.x * b.x + a.y * b.y;}
inline double vecLen(Vec x) { return sqrt(dotDet(x, x));}
inline Point normal(Vec x) { return Point(-x.y, x.x) / vecLen(x);}
Point lineIntersect(Point P, Vec v, Point Q, Vec w) {
Vec u = P - Q;
double t = crossDet(w, u) / crossDet(v, w);
return P + v * t;
}
inline Point getMid(Point a, Point b) { return (a + b) / 2.0;}
struct Circle {
Point c;
double r;
Circle() {}
Circle(Point c, double r) : c(c), r(r) {}
} ;
Circle getCircle(Point a, Point b, Point c) {
Vec v1 = b - a, v2 = c - a;
if (sgn(dotDet(b - a, c - a)) <= 0) return Circle(getMid(b, c), vecLen(b - c) / 2.0);
if (sgn(dotDet(a - b, c - b)) <= 0) return Circle(getMid(a, c), vecLen(a - c) / 2.0);
if (sgn(dotDet(a - c, b - c)) <= 0) return Circle(getMid(a, b), vecLen(a - b) / 2.0);
Point ip = lineIntersect(getMid(a, b), normal(v1), getMid(a, c), normal(v2));
return Circle(ip, vecLen(ip - a));
}
int andrew(Point *pt, int n, Point *ch) {
sort(pt, pt + n);
int m = 0;
for (int i = 0; i < n; i++) {
while (m > 1 && sgn(crossDet(ch[m - 2], ch[m - 1], pt[i])) <= 0) m--;
ch[m++] = pt[i];
}
int k = m;
for (int i = n - 2; i >= 0; i--) {
while (m > k && sgn(crossDet(ch[m - 2], ch[m - 1], pt[i])) <= 0) m--;
ch[m++] = pt[i];
}
if (n > 1) m--;
return m;
}
const int N = 555;
Point pt[N], ch[N];
int rnd[N];
void randPoint(Point *pt, int n) {
for (int i = 0; i < n; i++) rnd[i] = (rand() % n + n) % n;
for (int i = 0; i < n; i++) swap(pt[i], pt[rnd[i]]);
}
inline bool inCircle(Point p, Circle C) { return sgn(vecLen(C.c - p) - C.r) <= 0;}
int main() {
int n;
while (cin >> n && n) {
for (int i = 0; i < n; i++) scanf("%lf%lf", &pt[i].x, &pt[i].y);
n = andrew(pt, n, ch);
randPoint(ch, n);
Circle ans = Circle(ch[0], 0.0), tmp;
for (int i = 0; i < n; i++) {
if (inCircle(ch[i], ans)) continue;
ans = Circle(ch[i], 0.0);
for (int j = 0; j < i; j++) {
if (inCircle(ch[j], ans)) continue;
ans = Circle(getMid(ch[i], ch[j]), vecLen(ch[i] - ch[j]) / 2.0);
for (int k = 0; k < j; k++) {
if (inCircle(ch[k], ans)) continue;
ans = getCircle(ch[i], ch[j], ch[k]);
}
}
}
printf("%.2f
", ans.r + 0.5);
}
return 0;
}