#include<stdio.h>
#include<math.h>
int main()
{
double x1,x2,x3,y1,y2,y3,a1,a2,b1,b2,c1,c2,h,k,r,ans,d;
while(scanf("%lf%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&x3,&y3)==6)
{
a1=2*(x2-x1);
a2=2*(x3-x2);
b1=2*(y2-y1);
b2=2*(y3-y2);
c1=x1*x1+y1*y1-x2*x2-y2*y2;
c2=x2*x2+y2*y2-x3*x3-y3*y3;
d=a1*b2-a2*b1;
h=(b1*c2-b2*c1)/d;
k=(a2*c1-a1*c2)/d;
r=sqrt((h-x1)*(h-x1)+(k-y1)*(k-y1));
ans=2*3.141592653589793*r;
printf("%.2lf\n",ans);
}
return 0;
}
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