/************************************************
* Author        :Running_Time
* Created Time  :2015/11/10 星期二 11:24:09
* File Name     :UVA_11168.cpp************************************************/#include <bits/stdc++.h>
using namespace std;#define lson l, mid, rt << 1
#define rson mid + 1, r, rt << 1 | 1
typedef long long ll;
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;
const double EPS = 1e-10;
const double PI = acos (-1.0);
int dcmp(double x)  {if (fabs (x) < EPS) return 0;else    return x < 0 ? -1 : 1;
}
struct Point    {double x, y;Point () {}Point (double x, double y) : x (x), y (y) {}Point operator - (const Point &r) const {       //向量减法return Point (x - r.x, y - r.y);}Point operator * (double p) const {       //向量乘以标量return Point (x * p, y * p);}Point operator / (double p) const {       //向量除以标量return Point (x / p, y / p);}Point operator + (const Point &r) const {return Point (x + r.x, y + r.y);}bool operator < (const Point &r) const {return x < r.x || (x == r.x && y < r.y);}bool operator == (const Point &r) const {return dcmp (x - r.x) == 0 && dcmp (y - r.y) == 0;}
};
typedef Point Vector;
Point read_point(void)  {double x, y;    scanf ("%lf%lf", &x, &y);return Point (x, y);
}
double dot(Vector A, Vector B)  {       //向量点积return A.x * B.x + A.y * B.y;
}
double cross(Vector A, Vector B)    {       //向量叉积return A.x * B.y - A.y * B.x;
}
double length(Vector V) {return sqrt (dot (V, V));
}
vector<Point> convex_hull(vector<Point> ps) {sort (ps.begin (), ps.end ());ps.erase (unique (ps.begin (), ps.end ()), ps.end ());int n = ps.size (), k = 0;vector<Point> qs (n * 2);for (int i=0; i<n; ++i) {while (k > 1 && cross (qs[k-1] - qs[k-2], ps[i] - qs[k-2]) <= 0)    k--;qs[k++] = ps[i];}for (int t=k, i=n-2; i>=0; --i) {while (k > t && cross (qs[k-1] - qs[k-2], ps[i] - qs[k-2]) <= 0)    k--;qs[k++] = ps[i];}qs.resize (k-1);return qs;
}double sqr(double x)    {return x * x;
}int main(void)    {int T, cas = 0;  scanf ("%d", &T);while (T--) {int n;  scanf ("%d", &n);vector<Point> ps;double x, y, sx = 0, sy = 0;for (int i=0; i<n; ++i) {scanf ("%lf%lf", &x, &y);sx += x;    sy += y;ps.push_back (Point (x, y));}vector<Point> qs = convex_hull (ps);if ((int) qs.size () <= 2)  {printf ("Case #%d: %.3f\n", ++cas, 0.0);    continue;}double mn = 1e9;qs.push_back (qs[0]);for (int i=0; i<qs.size ()-1; ++i)    {double A = qs[i].y - qs[i+1].y;double B = qs[i+1].x - qs[i].x;double C = -A * qs[i].x - B * qs[i].y;double tmp = fabs (A * sx + B * sy + n * C) / sqrt (sqr (A) + sqr (B));if (mn > tmp)   mn = tmp;}printf ("Case #%d: %.3f\n", ++cas, mn / n);}//cout << "Time elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << " s.\n";return 0;
}