#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <list>
#include <set>
#include <map>
#include <algorithm>
#include <functional>

using namespace std;


int main()
{
  ifstream cin("circle2.txt");

  while(true)
    {
      int n;
      double x[100],y[100];
      cin >> n;
      
      if(n == 0)break;

      for(int i = 0;i < n;i++)
	cin >> x[i] >> y[i];

      int count = 0;

      int N = 1000;
      for(int i = 0;i < N;i++)
      for(int j = 0;j < N;j++)
	{
	  double a = 10.0*i/(double)N;
	  double b = 10.0*j/(double)N;

	  for(int k = 0;k < n;k++)
	    {
	      if((x[k] - a)*(x[k] - a) + (y[k] - b)*(y[k] - b) < 1.0)
		{
		  count++;
		  break;
		}
	    }


	}

      double ans = 100.0 * count /(double)N / (double)N;

      printf("%.2f\n",ans);

    }

  return 0;

}