#include<cmath>
#include<cstdio>
#include<cstring>
#include<stdlib.h>
#include<algorithm>
using namespace std;
double distance(double x1,double y1,double x2,double y2)
{
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
int main()
{
    //freopen("in.txt","r",stdin);
    double PI=2*asin(1.0);
    double x1,y1,r1;
    double x2,y2,r2;
    double dis,r,cosa,cosb;
    double a,b,c,d,ans;
    while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&r1,&x2,&y2,&r2)!=EOF)
    {
        dis=distance(x1,y1,x2,y2);
        if(dis>=r1+r2||r1==0||r2==0)//两圆相离，外切时，相交面积为0
            ans=0;
        else if(dis<=fabs(r1-r2))//两圆内含，内切时，相交面积为较小圆的面积
        {
            r=r1<r2?r1:r2;
            ans=r*r*PI;
        }
        else//两圆相交时
        {
            cosa=acos((r1*r1+dis*dis-r2*r2)/(2*r1*dis));
            cosb=acos((r2*r2+dis*dis-r1*r1)/(2*r2*dis));//余弦公式求出两圆连线和半径的夹角
            a=r1*r1*cosa;
            b=r2*r2*cosb;//扇形面积
            c=r1*r1*cos(cosa)*sin(cosa);
            d=r2*r2*cos(cosb)*sin(cosb);//三角形面积
//            s1=0.5*r1*r1*(cos1-sin(cos1));
//            s2=0.5*r2*r2*(cos2-sin(cos2));
            ans=(a+b)-(c+d);//这里用两个扇形的面积之和减去三角形之和，是因为相交的情况分为两个圆的圆心是否在同一个圆里两种情况
        } 
        printf("%.3lf\n",ans);
    }
    return 0;
}