#include "stdio.h"
#include "math.h"
#define PI 3.1415926536
int main()
{
	double x1,y1,r1,x2,y2,r2,r;
	double p,ang1,ang2,d1,d2,D1,D2,area;
	scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&r1,&x2,&y2,&r2);
	D1=(x1-x2)*(x1-x2)+(y1-y2)*(y1-y2);
	if((r1+r2)*(r1+r2)<=D1) printf("0.000\n");
	else if(D1<=fabs(r1-r2))
	{
		D2=(r1>r2)?r2:r1;
		printf("%.3lf",PI*D2*D2);	
	}
	else
	{
		D1=sqrt(D1);
		D2=(r1*r1-r2*r2)/D1;
		d1=(D1+D2)/2;
		d2=(D1-D2)/2;
		p=sqrt(r1*r1-d1*d1);
		ang1=acos(d1/r1);	
		ang2=acos(d2/r2);
		area=r1*r1*ang1+r2*r2*ang2-p*(d1+d2);
		area=(int)(area*1000+0.5)/1000.0;
		printf("%.3lf\n",area);	
	}
//	getch();	
	return 0;
}