#include <stdio.h>
#include <stdlib.h>
#include <math.h>

double x[1000], y[1000];

double dist(int i, int j)
{
  return sqrt((x[i]-x[j])*(x[i]-x[j]) + (y[i]-y[j])*(y[i]-y[j]));
}

double angle(double x1, double y1, double x2, double y2)
{
  double a = atan2(y2 - y1, x2 - x1);
  double pi = atan2(0, -1);
  if (a < 0) a = 2*pi + a;
  return a;
}

double angledistance(int i, int j, int k)
{
  double ad = angle(x[j], y[j], x[k], y[k]) - angle(x[i], y[i], x[j], y[j]);
  double pi = atan2(0, -1);
  while (ad > 2*pi) ad = ad - 2*pi;
  while (ad < 0) ad = ad + 2*pi;
  return ad;
}

void main(void)
{
  int z, k, n, i, b, b0, c, d;
  float xx, yy;
  double peri;
  
  scanf ("%d\n", &z);
  for (k = 1; k <= z; k ++)
    {
      scanf ("%d\n", &n);
      for (i = 0; i < n; i ++)
	{
	  scanf ("%f %f\n", &xx, &yy); 
	  x[i] = (double) xx; y[i] = (double) yy;
	}
      
      for (i = 0, b = 0; i < n; i ++)
	if (y[i] < y[b] || (y[i] == y[b] && x[i] < x[b])) b = i;
      b0 = b;
      for (i = 0, c = -1; i < n; i ++)
	if (i != b && (c == -1 || angle(x[b], y[b], x[i], y[i]) 
		       < angle(x[b], y[b], x[c], y[c])))
	  c = i;
      peri = dist(b, c);
      while (c != b0)
	{ 
	  for (i = 0, d = -1; i < n; i ++)
	    if (i != b && i != c && (d == -1 || angledistance(b, c, i) < angledistance(b, c, d)))
	      d = i;
	  peri += dist(c, d);
	  b = c;
	  c = d;
	}
      printf ("Data set %d: %.3f\n", k, peri);
    }
}