#include <iostream>

 using namespace std;

 #include<cmath>

 #include<stdio.h>

 #define PI 3.141593

 struct point//点

 {

     double x,y;

 };

 struct circle//圆

 {

     point center;

     double r;

 };

 float dist(point a,point b)//求圆心距

 {

     return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));

 }

 int main()

 {

     circle a,b;

     while(cin>>a.center.x>>a.center.y>>a.r>>b.center.x>>b.center.y>>b.r)

     {

         if((dist(a.center,b.center)+min(a.r,b.r))<=max(a.r,b.r))//两圆内交或包含

             {

                 if(a.r<b.r) printf("%.3lf\n",PI*a.r*a.r);

                 else printf("%.3lf\n",PI*b.r*b.r);

             }

         else if(dist(a.center,b.center)>=(a.r+b.r))//两圆外交或相离

             cout<<"0.000"<<endl;

         else

         {

             double length=dist(a.center,b.center);

             double d1=*acos((a.r*a.r+length*length-b.r*b.r)/(*a.r*length)); //求两扇形圆心角

             double d2=*acos((b.r*b.r+length*length-a.r*a.r)/(*b.r*length));

             double area1=a.r*a.r*d1/-a.r*a.r*sin(d1)/;

             //根据圆心角求扇形面积，减去三角形面积，得到相交部分面积

             //扇形面积：S=PI*r*r*θ/(2*PI)  三角形面积：S=1/2*a*c*sin(B)

             double area2=b.r*b.r*d2/-b.r*b.r*sin(d2)/;

             double area=area1+area2;

             printf("%.3lf\n",area);

         }

     }

     return ;

 }