#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#define MN 50000
#define eps 1e-17
#define ld long double
using namespace std;
inline int read()
{int x = 0 , f = 1; char ch = getchar();while(ch < '0' || ch > '9'){ if(ch == '-') f = -1;  ch = getchar();}while(ch >= '0' && ch <= '9'){x = x * 10 + ch - '0';ch = getchar();}return x * f;
}struct P
{ld x,y;P(ld _x=0,ld _y=0):x(_x),y(_y){}P operator +(P b){return P(x+b.x,y+b.y);}P operator -(P b){return P(x-b.x,y-b.y);}P operator *(ld b){return P(x*b,y*b);}ld operator^(P b){return x*b.y-b.x*y;}
}p[MN+5];
struct L
{P p,v;ld slop;L(){}L(P x,P y):p(x),v(y){slop=atan2(y.y,y.x);}P operator *(L y){P b=p-y.p;ld t=(y.v^b)/(v^y.v);return p+v*t;}bool operator <(const L&y)const{return slop<y.slop;}bool left(P y){return (v^(y-p))>eps;}
}q[MN+5],s[MN+5];
int n,top,tail;void solve()
{q[top=tail=1]=s[1];for(int i=2;i<=n;i++){while(top>tail&&!s[i].left(p[top])) --top;while(top>tail&&!s[i].left(p[tail+1])) ++tail;if(fabs(s[i].slop-q[top].slop)<eps)q[top]=s[i].left(q[top].p)?q[top]:s[i];else q[++top]=s[i];p[top]=q[top]*q[top-1];}while(top>tail&&!q[tail].left(p[top])) --top;
}int main()
{n=read();for(int i=1;i<=n;i++){double x,y,x2,y2;scanf("%lf%lf%lf%lf",&x,&y,&x2,&y2);s[i]=L(P(x,y),P(x2-x,y2-y));}s[++n]=L(P(0,0),P(10000,0));s[++n]=L(P(10000,0),P(0,10000));s[++n]=L(P(10000,10000),P(-10000,0));s[++n]=L(P(0,10000),P(0,-10000));sort(s+1,s+n+1);solve();p[tail]=q[top]*q[tail];if(top-tail<2) return 0*puts("0.0"); ld ans=p[top]^p[tail];for(int i=tail;i<top;i++) ans+=p[i]^p[i+1];printf("%.1lf\n",(double)fabs(ans)/2.0);return 0;
}