1 #include<cstdio>
 2 #include<cmath>
 3 #include<algorithm>
 4 #include<iostream>
 5 using namespace std;
 6 
 7 struct circle
 8 {
 9   double x,y,r;
10 };
11 double dist(circle a,circle b)
12 {
13   return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
14 }
15 int main()
16 {
17    circle a,b;
18    double d,p,area,sb,sa;
19   while(scanf("%lf%lf%lf%lf%lf%lf",&a.x,&a.y,&a.r,&b.x,&b.y,&b.r)!=EOF)
20   {
21     d=dist(a,b);
22     double rr=min(a.r,b.r);
23     if(d<=abs(a.r-b.r))   //内含或者内切
24        area=acos(-1.0)*rr*rr;
25     else
26        if(d>=a.r+b.r)
27           area=0.0;
28     else{
29          p=(a.r+b.r+d)/2.0;
30       sa=acos((a.r*a.r+d*d-b.r*b.r)/(2.0*a.r*d));
31       sb=acos((b.r*b.r+d*d-a.r*a.r)/(2.0*b.r*d));
32         area=sa*a.r*a.r+sb*b.r*b.r-2*sqrt(p*(p-a.r)*(p-b.r)*(p-d));
33     }
34     printf("%.3lf\n",area);
35   }
36  return 0;
37 }