#include <iostream>using namespace std;#include<cmath>#include<iomanip>#include<algorithm>int main(){    double d,t,t1,s,x,y,xx,yy,r,rr;    while(cin>>x>>y>>r)    {        cin>>xx>>yy>>rr;        d=sqrt((x-xx)*(x-xx)+(y-yy)*(y-yy));        if(d>=r+rr) s=0;        else if(d<=fabs(r-rr)) s=min(acos(-1.0)*r*r,acos(-1.0)*rr*rr);        else           {t=(r*r+d*d-rr*rr)/2.0/d;        t1=sqrt(r*r-t*t);        s=-d*t1+r*r*acos(t/r)+rr*rr*acos((d-t)/rr);        }        cout<<fixed<<setprecision(3)<<s<<endl;    }    return 0;}