1 #include <iostream>
 2 #include <string>
 3 #include <map>
 4 #include <stdio.h>
 5 #include <math.h>
 6 using namespace std;
 7 #define pi acos(-1)
 8 
 9 
10 main()
11 {
12      double x1, y1, x2, y2, r1, r2;
13      while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&r1,&x2,&y2,&r2)==6){
14          double d=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
15          if(d>=(r1+r2)){
16              printf("0.000\n");continue;
17          }
18         if(d<=(max(r1,r2)-min(r1,r2))){
19             printf("%.3lf\n",min(r1,r2)*min(r1,r2)*pi);continue;
20         } 
21          double a1=acos((r1*r1+d*d-r2*r2)/(2*r1*d));
22          double a2=acos((r2*r2+d*d-r1*r1)/(2*r2*d));
23          double s1=a1*r1*r1;
24          double s2=a2*r2*r2;
25          double s=r1*d*sin(a1);
26          printf("%.3lf\n",s1+s2-s);
27      }
28 }