#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
using namespace std;
double x,y,x2,y2,r1,r2,R1,R2,d1,a1,b1,Sbcd,Sacd,Sabcd,So1,So2,ans;
double pi=3.1415926535897932384626433832795;
double dist(double x, double y, double x2, double y2)
{
    return sqrt((x2-x)*(x2-x)+(y2-y)*(y2-y));
}
double sech(double R1, double R2)
{
    if(R1+R2<d1) return 0;
    if(R1==0||R2==0) return 0;
    a1=acos((double)(-R2*R2+R1*R1+d1*d1)/(2*d1*R1))*180.0/pi;
	b1=acos((double)(-R1*R1+R2*R2+d1*d1)/(2*d1*R2))*180.0/pi;
	Sbcd=(b1/180)*pi*R2*R2;
	Sacd=(a1/180)*pi*R1*R1;
	Sabcd=sin(a1*pi/180.0)*R1*d1;
	return Sbcd+Sacd-Sabcd;
}
int main()
{
    freopen("circles.in","r",stdin);
    freopen("circles.out","w",stdout);
	scanf("%lf%lf%lf%lf",&x,&y,&r1,&R1);
	scanf("%lf%lf%lf%lf",&x2,&y2,&r2,&R2);
	d1=dist(x,y,x2,y2);
	So1=pi*R1*R1-pi*r1*r1;
	So2=pi*R2*R2-pi*r2*r2;
	if(R1-R2>=d1) {printf("%lf\n",pi*R1*R1-pi*r1*r1-pi*r2*r2+sech(r1,r2)); return 0;}
	else if(R2-R1>=d1) {printf("%lf\n",pi*R2*R2-pi*r1*r1-pi*r2*r2+sech(r1,r2)); return 0;}
	else ans=sech(R1,R2);
	if(R1+R2<=d1) ans=0;
	if(r1+R2>d1&&R2-r1<d1)
	{
	    ans-=sech(r1,R2);
	}
	else if(R2-r1>=d1)
	{
	    ans-=pi*r1*r1;
	}
	if(R1+r2>d1&&R1-r2<d1)
	{
	    ans-=sech(R1,r2);
	}
	else if(R1-r2>=d1)
	{
	    ans-=pi*r2*r2;
	}
	if(r1+r2>=d1) ans+=sech(r1,r2);
	printf("%lf\n",So1+So2-ans);
	return 0;
}