LOJ 1433

#include <stdio.h>
#include <math.h>
int main() {
    int n,i;
    double ox,oy,ax,ay,bx,by,r,x,X,S;
    scanf("%d",&n);
    for(i=1;i<=n;i++){
        scanf("%lf %lf %lf %lf %lf %lf",&ox,&oy,&ax,&ay,&bx,&by);
        x = sqrt((ax-bx)*(ax-bx)+(ay-by)*(ay-by));
        r = sqrt((ax-ox)*(ax-ox)+(ay-oy)*(ay-oy));
        X = acos((r*r+r*r-x*x)/(2*r*r));
        S = r*X;
        printf("Case %d: %.5lf\n",i,S);
    }
    return 0;
}