#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define PI acos(-1.0)
using namespace std;
double solve(double x1,double y1,double x2,double y2,double r1,double r2)
{
	double d=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
	if(d>r1+r2)
	return 0;
	if(r1>=d+r2)
	return PI*r2*r2;
	if(r2>=d+r1)
	return PI*r1*r1;
	double angle1=acos((r1*r1+d*d-r2*r2)/(2*r1*d));
	double angle2=acos((r2*r2+d*d-r1*r1)/(2*r2*d));
	return angle1*r1*r1+angle2*r2*r2-r1*d*sin(angle1);
	
}
int main()
{
	double x1,y1,x2,y2,r1,r2;
	while(~scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&r1,&x2,&y2,&r2))
	{
		printf("%.3f\n",solve(x1,y1,x2,y2,r1,r2));
	}
}