//#pragma comment(linker, "/STACK:16777216") //for c++ Compiler#include <stdio.h>#include <iostream>#include <cstring>#include <cmath>#include <stack>#include <queue>#include <vector>#include <algorithm>#define ll long long#define Max(a,b) (((a) > (b)) ? (a) : (b))#define Min(a,b) (((a) < (b)) ? (a) : (b))#define Abs(x) (((x) > 0) ? (x) : (-(x)))#define eps 1e-11#define zero(a) fabs(a)<epsusing namespace std;const int INF = 0x3f3f3f3f;const int N = 20005;struct Point{    double x,y;}p[N*2];struct Segment{    Point s,e;    double angle;    void get_angle(){angle=atan2(e.y-s.y,e.x-s.x);}}seg[N];int m;//叉积为正说明，p2在p0-p1的左侧double xmul(Point p0,Point p1,Point p2){    return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);}Point Get_Intersect(Segment s1,Segment s2){    double u=xmul(s1.s,s1.e,s2.s),v=xmul(s1.e,s1.s,s2.e);    Point t;    t.x=(s2.s.x*v+s2.e.x*u)/(u+v);t.y=(s2.s.y*v+s2.e.y*u)/(u+v);    return t;}bool cmp(Segment s1,Segment s2){    //先按极角排序    if(s1.angle>s2.angle) return true;    //极角相等，内侧的在前    else if(zero(s1.angle-s2.angle)&&xmul(s2.s,s2.e,s1.e)>-eps) return true;    return false;}void HalfPlaneIntersect(Segment seg[],int n){    sort(seg,seg+n,cmp);    int tmp=1;    for(int i=1;i<n;i++)        if(!zero(seg[i].angle-seg[tmp-1].angle))            seg[tmp++]=seg[i];    n=tmp;    Segment deq[N];    deq[0]=seg[0];deq[1]=seg[1];    int head=0,tail=1;    for(int i=2;i<n;i++){        while(head<tail&&xmul(seg[i].s,seg[i].e,Get_Intersect(deq[tail],deq[tail-1]))<-eps) tail--;        while(head<tail&&xmul(seg[i].s,seg[i].e,Get_Intersect(deq[head],deq[head+1]))<-eps) head++;        deq[++tail]=seg[i];    }    while(head<tail&&xmul(deq[head].s,deq[head].e,Get_Intersect(deq[tail],deq[tail-1]))<-eps) tail--;    while(head<tail&&xmul(deq[tail].s,deq[tail].e,Get_Intersect(deq[head],deq[head+1]))<-eps) head++;    if(head==tail) return;    m=0;    for(int i=head;i<tail;i++)        p[m++]=Get_Intersect(deq[i],deq[i+1]);    if(tail>head+1)        p[m++]=Get_Intersect(deq[head],deq[tail]);}double Get_area(Point p[],int &n){    double area=0;    for(int i=1;i<n-1;i++)        area+=xmul(p[0],p[i],p[i+1]);    return fabs(area)/2.0;}int main(){    int n;    while(scanf("%d",&n)!=EOF){        seg[0].s.x=0;seg[0].s.y=0;seg[0].e.x=10000;seg[0].e.y=0;seg[0].get_angle();        seg[1].s.x=10000;seg[1].s.y=0;seg[1].e.x=10000;seg[1].e.y=10000;seg[1].get_angle();        seg[2].s.x=10000;seg[2].s.y=10000;seg[2].e.x=0;seg[2].e.y=10000;seg[2].get_angle();        seg[3].s.x=0;seg[3].s.y=10000;seg[3].e.x=0;seg[3].e.y=0;seg[3].get_angle();        for(int i=0;i<n;i++){            scanf("%lf%lf%lf%lf",&seg[i+4].s.x,&seg[i+4].s.y,&seg[i+4].e.x,&seg[i+4].e.y);            seg[i+4].get_angle();        }        HalfPlaneIntersect(seg,n+4);        printf("%.1f\n",Get_area(p,m));    }    return 0;}