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#include <cassert>
#include <iostream>
#include <algorithm>
#include <complex>
#include <tuple>
#include <cmath>
#include <iomanip>
using namespace std;
using T = long double;
using pt = complex<T>;
#define FOR(i, n) for(int i = 0, __n = n; i < __n; i++)
// #define DEBUG true

#ifdef DEBUG
#define LOG(x) cerr << x << endl;
#else
#define LOG(x)
#endif

#ifndef DEBUG
#define DEBUG false
#endif

const int MAXN = 100;
int n;

T dot(pt v, pt w) {return (conj(v) * w).real();}
T cross(pt v, pt w) {return (conj(v) * w).imag();}

struct line {
  pt p, q;
  line() {}
  line(pt p, pt q) : p(p), q(q) {}
  pt vec() const {
    return q - p;
  }
  T c() const {
    return cross(vec(), p);
  }
  friend ostream& operator<<(ostream& os, const line& dt);  
} V[MAXN]; 
  
ostream& operator<<(ostream& os, const line& l) {  
  os << l.p << "->" << l.q;
  return os;  
}  

T orient(line ab, pt c) {return cross(ab.q - ab.p,c - ab.p);}
bool half(pt p) {
  assert(p != pt(0));
  return p.imag() > 0 || (p.imag() == 0 && p.real() < 0);
}
bool angularCompare(pt v, pt w) {
  return make_tuple(half(v), 0) < make_tuple(half(w), cross(v, w));
}

bool angularCompareLine(const line & a, const line & b) {
  return angularCompare(a.vec(), b.vec());
}

pt inter(const line & l1, const line & l2) {
  T d = cross(l1.vec(), l2.vec());
  if (d == 0) {
    
    LOG("NO INTER " << l1 << " " << l2);
    cout << 0 << endl;
    exit(0);
  }
  // assert (d != 0);
  return (l2.vec() * l1.c() - l1.vec() * l2.c()) / d;
}

bool parallel(const line & l1, const line & l2) {
  return cross(l1.vec(), l2.vec()) == 0;
}



bool isCandidate(line a) {
  int online = 0;
  FOR(i, n) {
    T o1 = orient(a, V[i].p);
    T o2 = orient(a, V[i].q);
    if (o1 < 0 && o2 < 0) {
      return false;
    } else {
      if (o1 == 0  && o2 <= 0 || o2 == 0 && o1 <= 0) {
        online++;
      }
    }
  }

  if (online < 2) return false;
  return true;
}


int main() {
  cin >> n;
  FOR (i, n) {
    int a, b;
    cin >> a >> b;
    V[i].p = pt(a, b);
    cin >> a >> b;
    V[i].q = pt(a, b);
  }
  vector<line> candidates;
  FOR (i, n) {
    FOR (j, n) if(i != j) {
      line t[] = {
        line(V[i].p, V[j].p),
        line(V[i].p, V[j].q),
        line(V[i].q, V[j].p),
        line(V[i].q, V[j].q),
      };
      FOR(k, 4) {
        if (isCandidate(t[k])) {
          LOG("CANDIDATE: " << t[k]);
          candidates.push_back(t[k]); 
        } else {
          LOG("NOT CANDIDATE: " << t[k]);
        }
      }
    }
  }

  sort(candidates.begin(), candidates.end(), angularCompareLine);

  vector<line> bounds(1, candidates[0]);
  LOG(bounds.back() << " INIT");

  for (int i = 1; i < candidates.size(); i++) {
    const line & l = candidates[i];
    if (DEBUG) {
      cerr << endl << "   " << i << "  > " << l << " < " << endl;
      FOR(i, bounds.size()) {
        cerr << bounds[i] << " ";
      }
      cerr << endl;
    }
    if (parallel(l, bounds.back())) {
      LOG("> PARALLEL " << l << " " << bounds.back());
      if (orient(bounds.back(), l.p) <= 0) {
        LOG(l << " PARALLEL IGNORE");
        //Ignoruj, jezeli linia jest po zlej stronie.
        continue;
      } else if(bounds.size() == 1) {
        LOG(l << " PARALLEL REPLACE SINGLE");
        //Jezeli mamy jedyną linię, to zastąp.
        bounds[0] = l;
        continue;
      }
      // w przeciwnym wypadku usuwamy ostatnią linię i dodajemy normalnie
      LOG("! " << bounds.back() << " PARALLEL POP");
      bounds.pop_back();
    }
    while (bounds.size() > 1) {
      const line& l1 = bounds[bounds.size()-2];
      const line& l2 = bounds[bounds.size()-1];
      pt p2 = inter(l2, l);
      if (orient(l1, p2) <= 0) {
        LOG("! " << bounds.back() << " POP");
        bounds.pop_back();
      } else {
        break;
      }
    }
    LOG(l << " PUSH");
    bounds.push_back(l);
  }


  int start = 0;
  while (bounds.size() > start + 2) {
    if (orient(bounds[bounds.size()-2], inter(bounds[start], bounds.back())) <= 0) {
      LOG("! " << bounds.back() << " POP OVERLAP BACK");
      bounds.pop_back();
    } else if (orient(bounds.back(), inter(bounds[start], bounds[start+1])) <= 0) {
      LOG("! " << bounds[start] << " POP OVERLAP FRONT");
      start++;
    } else {
      break;
    }
  }
  bounds.erase(bounds.begin(), bounds.begin() + start);



  vector<pt> nodes;
  FOR(i, bounds.size()) {
    nodes.push_back(inter(bounds[i], bounds[(i+1) % bounds.size()]));
  }

  T area = 0;
  FOR(i, nodes.size()) {
    area += cross(nodes[i], nodes[(i+1) % nodes.size()]);
  }

  FOR(i, nodes.size()) {
    LOG(nodes[i]);
  }
  if (area < 0 && nodes.size() == 3) area = 0;
  cout << std::setprecision(12) << std::fixed << area/2 << endl;

  return 0;
}