I get WA 13 again and again and I can not find a mistake. My main logic looks like this:
for(j=0;j<n;j++)
{l=(x[j]-X)*(x[j]-X)+(y[j]-Y)*(y[j]-Y)+(z[j]-Z)*(z[j]-Z);
if (l-D<1e-10) D=l;}
printf("%0.6f\n",acos((2-D)/2.0)*r);

I believe it is correct..So can anybody help me with finding a bug, please? Does anyone have a same problem?

I had exactly this kind of problem. WA13.

then I wrote:

double tmp= (2 - minL)/2.0;
tmp-=0.00000000001;
if (tmp<-1) tmp=-1;
return r*Math.acos(tmp);

and AC.
It is problem with precision, of course.

What is D ?