1 #include
     
       2 #include
      
        3 #include
       
         4 #include
        
          5 #define pi 3.1415926535897932384626433832795 6 using namespace std; 7 double area(double x1,double y1,double r1,double x2,double y2,double r2) 8 { 9     double d=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));10     double r=r1
         
          =r1+r2) return 0;12     if (d<=fabs(r1-r2)) return pi*r*r;13     double a1=acos((r1*r1+d*d-r2*r2)/(2.0*r1*d));14     double a2=acos((r2*r2+d*d-r1*r1)/(2.0*r2*d));15     double ans=0.0;16     ans-=r1*sin(a1)*d;17     ans+=r1*r1*a1+r2*r2*a2;18     return ans;19 }20 int main()21 {22     double x1,y1,r1,x2,y2,r2;23     while (~scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&r1,&x2,&y2,&r2))24         printf("%.3lf\n",area(x1,y1,r1,x2,y2,r2));25     return 0;26 }
         
        
       
      
     

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