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#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <set>
#include <math.h>

using namespace std;

struct point {
  double x;
  double y;

  bool operator== (const point & rhs) const{
    return rhs.x == x and rhs.y == y;
  }

  bool operator!= (const point & rhs) const{
    return ! (rhs == *this);
  }

};

struct tpoint {
  int mage;
  point loc;
};

struct mage {
  int numb;
  point t1;
  point t2;
};

struct anglesort 
{
  bool operator()(const pair<double,int>& t1, const pair<double,int>& t2) const {

    return t1.first < t2.first;
  }
};
struct pointsort 
{
  bool operator()(const tpoint& t1, const tpoint& t2) const {

    if(t1.loc.y == t2.loc.y){
      return t1.loc.x < t2.loc.x;
    }
    return t1.loc.y > t2.loc.y;
  }
};



double calcarea(const vector<point> & points){

  point avarage;
  for(const auto p : points){
    avarage.x += p.x;
    avarage.y += p.y;
  }

  avarage.x /= points.size();
  avarage.y /= points.size();

  double area = 0;

  for(int i = 0; i < points.size() - 1; i ++){

    double x1 = points[i].x,
           y1 = points[i].y,
           x2 = points[(i + 1)].x,
           y2 = points[(i + 1)].y;
    
    double areainc =( avarage.x * (y1 - y2) + x1 * (y2 - avarage.y) + x2 * (avarage.y - y1)) / 2.0;
    area += abs(areainc);
  }
  return abs(area);
  
}

double getangle(point orig, point toget){
  double angle =atan2(toget.x - orig.x, toget.y - orig.y);
  while(angle < 0){
    angle += 2 * M_PI;
  }
  return angle;
}


vector<pair<double, int>> calcangles(const vector<tpoint> & points, point cur, double sangle, int index = -1){
  vector<pair<double, int>> tbyangle;
  for(int i = 0; i < points.size(); i++){
    if(points[i].mage != index){
      double angle = getangle(cur, points[i].loc);
      angle -= sangle;
      while(angle < 0 ){
        angle += 2 * M_PI;
      }

      tbyangle.push_back({angle, points[i].mage});
    }

  }
  return tbyangle;
}

pair<bool, point> intersect(point a, point b, point c, point d){
  double x1 = a.x, x2 = b.x, x3 = c.x, x4 = d.x;
  double y1 = a.y, y2 = b.y, y3 = c.y, y4 = d.y;
  double denom = (x4 - x3) * (y1 - y2) - (x1 - x2) * (y4 - y3);
  if(denom == 0.0){
    return {false, {0.0, 0.0}};
  }
  double nom1 = (y3 - y4) * (x1 - x3) + (x4 - x3) * (y1 - y3); 
  double frac1 = nom1 / denom;
  double nom2 = (y1 - y2) * (x1 - x3) + (x2 - x1) * (y1 - y3); 
  double frac2 = nom2 / denom;
  if(frac1 >= 1.0 or frac1 <= 0.0  or frac2 >= 1.0 or frac2 <= 0.0){
    return {false, {0.0, 0.0}};
  }

  return {true, {x1 + frac1 * (x2 - x1), y1 + frac1 * (y2 - y1)}};

}

int main (){
  cout << fixed << setprecision(9);

  int n;
  cin >> n;
  vector<mage> mages;
  vector<tpoint> tpoints;
  unordered_map<int, point> tbynumb;
  for(int i = 0; i < n; i ++){
    mage cur;
    cur.numb = i;
    cin >> cur.t1.x >> cur.t1.y >> cur.t2.x >> cur.t2.y;
    mages.push_back(cur);
    tpoints.push_back({2 * i, cur.t1});
    tpoints.push_back({2 * i + 1, cur.t2});
    tbynumb[2 * i] = cur.t1;
    tbynumb[2 * i + 1] = cur.t2;
    
  }


  sort(tpoints.begin(), tpoints.end(), pointsort());
  int curpoint = tpoints[0].mage;
  {
    unordered_set<int> seen;
    for(auto cur : tpoints){
      if(seen.find(cur.mage / 2) != seen.end()){
        curpoint = cur.mage;
        break;
      }
      seen.insert(cur.mage / 2);
    }
  }
  double direction = 0.0;
  vector<point> shape;
  shape.push_back(tbynumb[curpoint]);
  vector<int> candidates = {};
  while(shape.size() == 1 or shape[0] != shape[shape.size() - 1]) {
    auto angles = calcangles(tpoints, tbynumb[curpoint], direction, curpoint);
    sort(angles.begin(), angles.end(), anglesort());
    unordered_set<int> seen;
    for (auto a : angles){
      int curmagenumber = a.second / 2;
      if(seen.find(curmagenumber) != seen.end()){
        if(shape.size() > 1){
          int rest = curpoint  % 2;
          rest = 1 - rest; // swap it!
          auto othertower = tbynumb[(curpoint/ 2)  * 2 + rest];
          auto intersection = intersect(othertower, tbynumb[a.second], shape[shape.size() - 2], tbynumb[curpoint]);
          if(intersection.first){
             shape[shape.size() - 1] = intersection.second;
          }
        }
        shape.push_back(tbynumb[a.second]);
        if(shape.size() > 2){
          auto intersection = intersect(shape[0], shape[1], shape[shape.size() -1], shape[shape.size() - 2]);
          if(intersection.first){
            shape[0] = intersection.second;
            shape[shape.size() - 1] = intersection.second;

          }
        }
        curpoint = a.second;
        direction += a.first;
        

        break;
      }
      seen.insert(a.second / 2);
    }


    set<pair<double,double>> seenp;
    for(int j = 0; j < shape.size() - 2; j ++){
      auto a = shape[j];
      if(seenp.find({a.x, a.y}) != seenp.end()){
        int first = 0, second = 0;
        for(int i = 0; i < shape.size(); i ++){
          if(shape[i].x == a.x and shape[i].y == a.y){
            first = second;
            second = i;
          }

        }

        vector<point> newshape = {shape.begin() + first, shape.begin() + second + 1};
        cout << calcarea(newshape) << endl;
        return 0;
      }
      seenp.insert({a.x, a.y});
    }
  }
  cout << calcarea(shape) << endl;
}