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

float dist (float x1, float y1, float x2, float y2)
{ return (x1-x2)*(x1-x2)+(y1-y2)*(y1-y2); }

int main (void)
{
  int K, k;
  int n, i;
  float x[1001], y[1001], x0, y0;
  float d;

  FILE *in = fopen ("cruise.in", "r"),
    *out = fopen("cruise.out", "w");

  fscanf (in, "%d\n", &K);

  for (k = 1; k <= K; k ++)
    {
      fprintf (out, "Data Set %d:\n", k);
      fscanf (in, "%d %f %f\n", &n, &x0, &y0);
      d = -1;
      for (i = 0; i < n; i ++) 
	{
	  fscanf (in, "%f %f\n", &x[i], &y[i]);
	  if (d < 0 || dist(x0, y0, x[i], y[i]) < d)
	    d = dist(x0, y0, x[i], y[i]);
	}
      for (i = 0; i < n; i ++)
	{
	  int j = (i+1)%n;
	  float u = ((x0-x[i])*(x[j]-x[i])+(y0-y[i])*(y[j]-y[i]))
	    / dist(x[i], y[i], x[j], y[j]);
	  if (0 < u && u < 1)
	    {
	      float xt = (1-u)*x[i] + u*x[j], yt=(1-u)*y[i] + u*y[j];
	      if (dist(x0, y0, xt, yt) < d) d = dist(x0, y0, xt, yt);
	    }
	}
      fprintf (out, "%0.2f\n\n", (float) sqrt((double) d));
      fscanf (in, "\n");
    }

  fclose (in); fclose (out);  
  return 0;
}