#include<bits/stdc++.h>
using namespace std;
#define pb push_back
#define eb emplace_back
//mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());
#define mod 998244353
#define ll long long
#define inf 0x3f3f3f3f
#define INF 0x3f3f3f3f3f3f3f3f
inline int read()
{
	char ch=getchar(); int nega=1; while(!isdigit(ch)) {if(ch=='-') nega=-1; ch=getchar();}
	int ans=0; while(isdigit(ch)) {ans=ans*10+ch-48;ch=getchar();}
	if(nega==-1) return -ans;
	return ans;
}
void print(vector<int> x){for(int i=0;i<(int)x.size();i++) printf("%d%c",x[i]," \n"[i==(int)x.size()-1]);}
const double eps=1e-11;
int sgn(double x)
{
	if(x<-eps) return -1;
	else if(x>eps) return 1;
	else return 0;
}
struct Vec
{
	double x,y;
	Vec(double a=0,double b=0) {x=a,y=b;}
	double norm() {return x*x+y*y;}
	double abs() {return sqrt(x*x+y*y);}
};
Vec rdvec()
{
	double x,y;
	scanf("%lf %lf",&x,&y);
	return Vec(x,y);
}
Vec operator + (const Vec &x,const Vec &y) {return Vec(x.x+y.x,x.y+y.y);}
Vec operator - (const Vec &x,const Vec &y) {return Vec(x.x-y.x,x.y-y.y);}
Vec operator * (const Vec &x,const double y) {return Vec(x.x*y,x.y*y);}
Vec operator / (const Vec &x,const double y) {return Vec(x.x/y,x.y/y);}
double dis(const Vec &x,const Vec &y) {return (x-y).abs();}
void print(Vec x) {printf("%.10lf %.10lf\n",x.x,x.y);}
double cdot(const Vec &x,const Vec &y) {return x.x*y.x+x.y*y.y;}
double cross(const Vec &x,const Vec &y) {return x.x*y.y-x.y*y.x;}
int ccw(Vec x,Vec y,Vec z)
{
	int w=sgn(cross(y-x,z-x));
	if(w==1) return 1; // ccw
	else if(w==-1) return -1; // cw;
	else return 0; // coline
}
struct Seg
{
	Vec s,t; // two points
	Seg(Vec x,Vec y) {s=x,t=y;}
	Seg() {}
	Vec d() {return t-s;}
	Vec point(double p) {return s+(t-s)*p;}
};
int parallel(Seg p,Seg q) {return sgn(cross(p.d(),q.d()))==0;}
Vec proj(Seg l,Vec x)
{
	double p=cdot(l.t-l.s,x-l.s)/(l.t-l.s).norm();
	return l.point(p);
}
int isintersect(Seg p,Seg q)
{
	if(max(p.s.x,p.t.x)<min(q.s.x,q.t.x)) return 0;
	if(max(q.s.x,q.t.x)<min(p.s.x,p.t.x)) return 0;
	if(max(p.s.y,p.t.y)<min(q.s.y,q.t.y)) return 0;
	if(max(q.s.y,q.t.y)<min(p.s.y,p.t.y)) return 0;
	if(ccw(q.s,p.s,p.t)*ccw(q.t,p.s,p.t)==1) return 0;
	if(ccw(p.s,q.s,q.t)*ccw(p.t,q.s,q.t)==1) return 0;
	return 1;
}
Vec crosspoint(Seg p,Seg q)
{
	double A=cross(p.t-p.s,q.t-q.s);
	double B=cross(p.t-p.s,p.t-q.s);
	return q.s+(q.t-q.s)*(B/A);
}
vector<Vec> halfPlane(vector<Seg> v) // left halfplanes
{
	sort(v.begin(),v.end(),[&](Seg x,Seg y){
		double ang1=atan2(x.d().y,x.d().x);
		double ang2=atan2(y.d().y,y.d().x);
		if(sgn(ang1-ang2)) return ang1<ang2;
		else return ccw(x.s,y.s,y.t)==1;
	});
	auto onRight=[&](Seg s,Vec x) {return ccw(s.s,x,s.t)>=0;};
	static Seg q[1005];
	static Vec p[1005];
	int l=0,r=0; q[0]=v[0];
	for(int i=1;i<(int)v.size();i++)
	{
		while(l<r&&onRight(v[i],p[r])) r--;
		while(l<r&&onRight(v[i],p[l+1])) l++;
		q[++r]=v[i];
		if(parallel(q[r],q[r-1]))
		{
			if(onRight(q[r],q[r-1].s)&&cdot(q[r].d(),q[r-1].d())<eps) return {};
			r--;
			if(!onRight(q[r],v[i].s)) q[r]=v[i];
		}
		if(l<r) p[r]=crosspoint(q[r],q[r-1]);
	}
	while(l<r&&onRight(q[l],p[r])) r--;
	if(r-l<=1) return {};
	p[l]=crosspoint(q[l],q[r]);
	return vector<Vec>(p+l,p+r+1);
}
double Area(vector<Vec> v) // ccw
{
	double ans=0;
	for(int i=1;i+1<(int)v.size();i++) ans+=cross(v[i]-v[0],v[i+1]-v[0]);
	return ans/2;
}
signed main()
{
	int n=read();
	vector<Seg> a;
	Vec v0(0,0),v1(10000,0),v2(10000,10000),v3(0,10000);
	a.emplace_back(v0,v1),a.emplace_back(v1,v2),a.emplace_back(v2,v3),a.emplace_back(v3,v0);
	for(int i=1;i<=n;i++)
	{
		Vec s=rdvec(),t=rdvec();
		a.emplace_back(s,t);
	}
	vector<Vec> ans=halfPlane(a);
	if(ans.empty()) printf("0.0\n");
	else printf("%.1lf\n",Area(ans));
	return 0;
}