/** @JUDGE_ID: GOKURI_SQUEEZE ??? C++ */
#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <fstream>
#include <complex>
#include <cmath>
using namespace std;

#define FNAME "circle.txt"
#define cin fin

const int NUM = 1000000;
const double PI = 3.1415926535;
double AREA_0;
double AREA_1;
double AREA_2;
double AREA_3;
double AREA_4;

double area1()
{
  double ret = 0.0;
  for (int i = 0; i < NUM; ++i) {
    double h = 0.5 / NUM;
    double x = 0.5 + h * i;
    double d = sqrt(1 - x * x) * h;
    ret += d;
  }

  return 4 * ret;
}

double area2()
{
  const double S2 = sqrt(0.5);
  
  double ret = 0.0;
  for (int i = 0; i < NUM; ++i) {
    double h = 1.0 / NUM;
    double x = h * i;
    // double d = sqrt(1 - x * x) * h;
    double d = (sqrt(1 - x * x) - (1 - sqrt(1 - (x - 1) * (x - 1)))) * h;
    ret += d;
  }

  return ret;
}

double area3()
{
  return (AREA_2 + AREA_4) / 2;
#if 0
  const double S2 = sqrt(0.5);
  
  double ret = 0.0;
  for (int i = 0; i < NUM; ++i) {
    double h = (S2 - 0.5) / NUM;
    double x = 0.5 + h * i;
    double d = (2 * sqrt(1 - x * x) - 1.0) * h;
    ret += d;
  }

  for (int i = 0; i < NUM; ++i) {
    double h = 0.5 / NUM;
    double x = h * i;
    double d = (sqrt(1 - x * x) - (1 - sqrt(1 - (x - 1) * (x - 1)))) * h;
    ret += d;
  }
  
  return ret;
#endif
}

double area4()
{
  const double S2 = sqrt(0.5);
  
  double ret = 0.0;
  for (int i = 0; i < NUM; ++i) {
    double h = (S2 - 0.5) / NUM;
    double x = 0.5 + h * i;
    double d = (sqrt(1 - x * x) - 0.5) * h;
    ret += d;
  }

  return 4 * ret;
}



double solve(const set<pair<int, int> > & points)
{
  int n0 = 0, n1 = 0, n2 = 0, n3 = 0, n4 = 0;

  for (set<pair<int, int> >::const_iterator it = points.begin();
       it != points.end(); ++it)
    {
      int i = it->first;
      int j = it->second;
      ++n0;

      bool ipjp = points.find(make_pair(i + 1, j + 1)) != points.end();
      bool imjp = points.find(make_pair(i - 1, j + 1)) != points.end();
      bool ijp  = points.find(make_pair(i    , j + 1)) != points.end();
      bool ipj  = points.find(make_pair(i + 1, j    )) != points.end();
      
      
      if (ijp) { ++n1; }
      if (ipj) { ++n1; }
      
      if (ipjp) { ++n2; }
      if (imjp) { ++n2; }

      if (ijp && ipj) { ++n3; }
      if (ijp && ipjp) { ++n3; }
      if (ipj && ipjp) { ++n3; }
      if (ipj && imjp) { ++n3; }

      if (ijp && ipj && ipjp) { ++n4; }
    }
  

#if 0
  cout << n0 << ' '
    << n1 <<  ' '
      << n2 << ' '
        << n3 << ' '
          << n4 << ' ' << endl;
#endif
  return n0 * AREA_0
    - n1 * AREA_1
      - n2 * AREA_2
        + n3 * AREA_3
          - n4 * AREA_4;
}

int main()
{
  ifstream fin(FNAME);
  if(!fin) return -1;

  AREA_0 = PI;
  AREA_1 = area1();  
  AREA_2 = area2();  
  AREA_4 = area4();
  AREA_3 = area3();  
#if 0
  cout << AREA_1 << ' '
       << AREA_2 << ' '
       << AREA_3 << ' '
       << AREA_4 << ' ' << endl;
#endif
  int N;
  int test = 0;
  while (cin >> N, N) {
    set<pair<int, int> > points;
    // vector<vector<int> > points(202, vector<int>(202));

    for (int i = 0; i < N; ++i) {
      int x, y; cin >> x >> y;
      points.insert(make_pair(x, y));
      // points[x][y] = 1;
    }

    double area = solve(points);
    char buf[32];
    sprintf(buf, "%.4f", area);
    cout << "Data set #" << (++test) << ":  ";
    cout << "Total area = " << buf << " square meters." << endl;
  }
  
  return 0;
}