// Maximum-TNT

#include <iostream>
#include <string>
#include <sstream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <complex>
#include <vector>
#include <set>
#include <algorithm>
#include <fstream>

using namespace std;

#define cin fin

const int BUFSIZE = 1024;
const double ERROR=1e-5;

ifstream fin("circle2.txt");
#define cmp_t complex<double>
int g_n;
vector<cmp_t> g_center;

bool operator<(pair<int,int> a,pair<int,int> b)
{
    return a.first < b.first || (a.first == b.first && a.second < b.second);
}

double Solve()
{
    set<pair<int,int> > inside;
    for(int i = 0 ; i < g_n ; i++)
    {
	cmp_t now= g_center[i];
	int x = (int)floor(now.real());
	int y = (int)floor(now.imag());
	for(int j = -100 ; j <= 100 ; j++)
	    for(int k = -100 ; k <= 100 ; k++)
	    {
		if(abs(now- cmp_t(x+j,y+k)) < 100+ERROR)
		{
		    inside.insert(make_pair(x+j,y+k));
		}
	    }
    }
    return ceil(0.01*inside.size())*0.01;
}

double Solve2()
{
    int count = 0;
    const int NUM=1000000;
    for(int i = 0 ; i < NUM ; i++)
    {
	double x = (rand()/(double)RAND_MAX)*10;
	double y = (rand()/(double)RAND_MAX)*10;
	cmp_t p(x,y);
	for(int j = 0 ; j < g_n ; j++)
	{
	    if(abs(g_center[j]-p) < 1+ERROR)
	    {
		count++;
		break;
	    }
	}
    }
    return (count/(double)NUM)*100;
}

int main()
{
    while(cin >> g_n , g_n)
    {
	double x,y;
	g_center.clear();
	for(int i = 0 ; i < g_n ; i++)
	{
	    cin >> x >> y;
	    x = floor(x*100+0.5+ERROR);
	    y = floor(y*100+0.5+ERROR);
	    g_center.push_back(cmp_t(x,y));
	}
	cout.setf(ios::fixed);
	cout.precision(2);
	cout << Solve() << endl;
// 	for(int i = 0 ; i < g_n ; i++)
// 	{
// 	    cin >> x >> y;
// 	    g_center.push_back(cmp_t(x,y));
// 	}
// 	cout.setf(ios::fixed);
// 	cout.precision(2);
// 	cout<< Solve2() << endl;
    }
    return 0;
}