#include<bits/stdc++.h>
using namespace std;

#define rep(i,a,n) for(int i=a;i<n;i++)
#define mem(a,n) memset(a,n,sizeof(a))
#define pb push_back
#define IO ios::sync_with_stdio(false);
typedef long long ll;
typedef double DBL;
const int N=5e2+5;
const int maxn=510;
const double eps=1e-4;
const int MOD=1e9+7;
const int dir[4][2]= {-1,0,1,0,0,-1,0,1}; ///上下左右
const int INF=0x3f3f3f3f;

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[maxn],temp[maxn];
    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;//面积交
    //return PolygonArea(a,na)+PolygonArea(b,nb)-res;//面积并
}
Point a[4],b[5];

int main()
{
    int x1,x2,x3,x4,y1,y2,y3,y4;
    while(~scanf("%d%d%d%d",&x1,&y1,&x2,&y2))
    {
        scanf("%d%d%d%d",&x3,&y3,&x4,&y4);
        a[0]=Point(x1,y1);
        a[1]=Point(x2,y1);
        a[2]=Point(x1,y2);

        b[0]=Point(x3,y3);
        b[1]=Point(x3,y4);
        b[2]=Point(x4,y4);
        b[3]=Point(x4,y3);
        printf("%.8f\n",fabs(SPIA(a,b,3,4)));
    }
    return 0;
}