> #include<iostream.h>
> #include<math.h>
> #include<iomanip.h>
> int main()
> {
> 	double x1,y1,r1,x2,y2,r2,r,a,b,c,d,e,f,s1,s2,s3,s4,s;
> 	while(cin>>x1>>y1>>r1>>x2>>y2>>r2)
> 	{
> 		r=pow((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2),0.5);
> 		if(r>=r1+r2)
> 			cout<<"0.000"<<endl;
> 		else if(r<=fabs(r1-r2))
> 		{
> 			r=r1>=r2?r1:r2;
> 			s=3.14159265358*r*r;
> 			cout<<setiosflags(ios::fixed)<<setprecision(3)<<s<<endl;
> 		}
> 			else
> 			{
> 				a=(r2*r2+r*r-r1*r1)/(2*r2*r);
> 				c=pow(1-a*a,0.5);
> 				s2=r2*a*r2*c;
> 				e=acos(a);
> 				e*=2;
> 				s1=e*r2*r2/2;
> 				b=(r1*r1+r*r-r2*r2)/(2*r1*r);
> 				d=pow(1-b*b,0.5);
> 				s4=r1*b*r1*d;
> 				f=acos(b);
> 				f*=2;
> 				s3=f*r1*r1/2;
> 				s=s1-s2+s3-s4;
> 				cout<<setiosflags(ios::fixed)<<setprecision(3)<<s<<endl;
> 			}
> 	}
> 	return 1;
> }