#include <fstream>
#include <iostream>
#include <stdlib.h>
#include <stdio.h>
using namespace std;

double sq(double d) { return d*d; }

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

  int n;
  while(cin>>n,n){
    double dat[10][2];
    int i,j;
    for (i=0;i<n;i++)
      cin>>dat[i][0]>>dat[i][1];

#define TRY 100000000
    int cnt=0;
    for (i++;i<TRY;i++){
      double x=(rand()%0xffff)/65536.0*10;
      double y=(rand()%0xffff)/65536.0*10;
      for (j=0;j<n;j++){
        if (sq(dat[j][0]-x)+sq(dat[j][1]-y)<=1.0){
          cnt++;
          break;
        }
      }
    }

    double ans=cnt/((double)TRY)*100.0;
    printf("%.2f\n",ans);
  }
  return 0;
}