#include <iostream>

#include <cstring>

#include <algorithm>

#include <queue>

#include <cstdio>

#include <cstdlib>

#include <cctype>

#include <math.h>

using namespace std;

#define memset(a,b) memset(a,b,sizeof(a))

#define N 1100000

typedef long long  ll;

#define PI 3.1415926

int main()

{

    double x1,y1,r1,x2,y2,r2;

    while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&r1,&x2,&y2,&r2)!=EOF)

    {

        double rr=min(r1,r2);

        double l=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));

        if(l>=r1+r2)

        {

            printf("0.000\n");

            continue;

        }

        else if(l<=fabs(r1-r2))

        {

            printf("%.3lf\n",acos(-1.0)*rr*rr);

            continue;

        }

        double cos1=(r1*r1+l*l-r2*r2)/(2.0*r1*l);

        double cos2=(r2*r2+l*l-r1*r1)/(2.0*r2*l);

        double ss1=r1*acos(cos1)*r1;///r1扇形的面积

        double ss2=r2*acos(cos2)*r2;

        double p=(r1+r2+l)/2.0;///

        double S=*sqrt(p*(p-r1)*(p-r2)*(p-l));///四边形的面积

        printf("%.3lf\n",ss1+ss2-S);

    }

    return ;

}