> #include<stdio.h>
> #include<string.h>
> #include<math.h>
> #define pi 3.14159265358
> int main(){
> 	int i,j,k,m,n;
> 	double x1,y1,r1,x2,y2,r2,r,r3,s,area;
> 	double A,B;
> 	while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&r1,&x2,&y2,&r2)!=EOF){
> 	    r=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
> 		if(r1<r2)
> 		  {  r3=r1;
> 		    r1=r2;
> 		    r2=r3;}
>        // printf("r1==%.3lf r2==%.3lf r=%.3lf\n",r1,r2,r);
> 		if(r>=r1+r2)
> 		    printf("0.000\n");//相离或相切 
> 		else if(r<=r1-r2){
> 		    printf("%.3lf\n",pi*r2*r2);	 
> 	    }				 
> 	    else {
> 		    A=acos((r1*r1+r*r-r2*r2)/(2*r1*r));
> 			B=acos((r2*r2+r*r-r1*r1)/(2*r*r2));
> 			s=(r1+r2+r)/2;
>             s=sqrt(s*(s-r1)*(s-r2)*(s-r));
> 	        area=A*r1*r1+B*r2*r2-2*s;
> 	    
> 	        printf("%.3lf\n",area);
> 	    }
>     }
> 	
> 	return 0;	
> }
>