#pragma comment(linker, "/STACK:1024000000,1024000000")#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>#include<vector>#include<map>#include<set>#include<queue>#include<stack>#include<iostream>using namespace std;typedef long long LL;const double pi=acos(-1.0),eps=1e-6;void File(){    freopen("D:\\in.txt","r",stdin);    freopen("D:\\out.txt","w",stdout);}template <class T>inline void read(T &x){    char c = getchar();    x = 0;    while(!isdigit(c)) c = getchar();    while(isdigit(c))    {        x = x * 10 + c - ‘0‘;        c = getchar();    }}const int maxn=555;const int maxisn=10;int dcmp(double x){    if(x>eps) return 1;    return x<-eps ? -1 : 0;}inline double Sqr(double x){    return x*x;}struct Point{    double x,y;    Point()    {        x=y=0;    }    Point(double x,double y):x(x),y(y) {};    friend Point operator + (const Point &a,const Point &b)    {        return Point(a.x+b.x,a.y+b.y);    }    friend Point operator - (const Point &a,const Point &b)    {        return Point(a.x-b.x,a.y-b.y);    }    friend bool operator == (const Point &a,const Point &b)    {        return dcmp(a.x-b.x)==0&&dcmp(a.y-b.y)==0;    }    friend Point operator * (const Point &a,const double &b)    {        return Point(a.x*b,a.y*b);    }    friend Point operator * (const double &a,const Point &b)    {        return Point(a*b.x,a*b.y);    }    friend Point operator / (const Point &a,const double &b)    {        return Point(a.x/b,a.y/b);    }    friend bool operator < (const Point &a, const Point &b)    {        return a.x < b.x || (a.x == b.x && a.y < b.y);    }    inline double dot(const Point &b)const    {        return x*b.x+y*b.y;    }    inline double cross(const Point &b,const Point &c)const    {        return (b.x-x)*(c.y-y)-(c.x-x)*(b.y-y);    }};Point LineCross(const Point &a,const Point &b,const Point &c,const Point &d){    double u=a.cross(b,c),v=b.cross(a,d);    return Point((c.x*v+d.x*u)/(u+v),(c.y*v+d.y*u)/(u+v));}double PolygonArea(Point p[],int n){    if(n<3) return 0.0;    double s=p[0].y*(p[n-1].x-p[1].x);    p[n]=p[0];    for(int i=1; i<n; i++)    {        s+=p[i].y*(p[i-1].x-p[i+1].x);    }    return fabs(s*0.5);}double CPIA(Point a[],Point b[],int na,int nb){    Point p[maxisn],temp[maxisn];    int i,j,tn,sflag,eflag;    a[na]=a[0],b[nb]=b[0];    memcpy(p,b,sizeof(Point)*(nb+1));    for(i=0; i<na&&nb>2; ++i)    {        sflag=dcmp(a[i].cross(a[i+1],p[0]));        for(j=tn=0; j<nb; ++j,sflag=eflag)        {            if(sflag>=0) temp[tn++]=p[j];            eflag=dcmp(a[i].cross(a[i+1],p[j+1]));            if((sflag^eflag)==-2)                temp[tn++]=LineCross(a[i],a[i+1],p[j],p[j+1]);        }        memcpy(p,temp,sizeof(Point)*tn);        nb=tn,p[nb]=p[0];    }    if(nb<3) return 0.0;    return PolygonArea(p,nb);}double SPIA(Point a[],Point b[],int na,int nb){    int i,j;    Point t1[4],t2[4];    double res=0.0,if_clock_t1,if_clock_t2;    a[na]=t1[0]=a[0];    b[nb]=t2[0]=b[0];    for(i=2; i<na; i++)    {        t1[1]=a[i-1],t1[2]=a[i];        if_clock_t1=dcmp(t1[0].cross(t1[1],t1[2]));        if(if_clock_t1<0) swap(t1[1],t1[2]);        for(j=2; j<nb; j++)        {            t2[1]=b[j-1],t2[2]=b[j];            if_clock_t2=dcmp(t2[0].cross(t2[1],t2[2]));            if(if_clock_t2<0) swap(t2[1],t2[2]);            res+=CPIA(t1,t2,3,3)*if_clock_t1*if_clock_t2;        }    }    return res;}Point a[222],b[222];Point aa[222],bb[222];int main(){    int n1,n2;    double x1,y1,x2,y2,x3,y3,x4,y4;    while(~scanf("%lf%lf%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3,&x4,&y4))    {        n1=3,n2=4;        a[0].x=x1; a[0].y=y1;        a[1].x=x1; a[1].y=y2;        a[2].x=x2; a[2].y=y1;        b[0].x=x3; b[0].y=y3;        b[1].x=x3; b[1].y=y4;        b[2].x=x4; b[2].y=y4;        b[3].x=x4; b[3].y=y3;        printf("%.6lf\n",abs(SPIA(a,b,n1,n2)));    }    return 0;}