#include<bits/stdc++.h>
#include<math.h>
#define pi 3.141592653589793
int main()
{
double x1,x2,y1,y2,x3,y3,a,b,c,s,radius,d,circle;
while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3) != EOF)
{
a=sqrt(pow((x1-x2),2)+pow((y1-y2),2));
b=sqrt(pow((x2-x3),2)+pow((y2-y3),2));
c=sqrt(pow((x3-x1),2)+pow((y3-y1),2));
s=(a+b+c)/2;
radius=a*b*c/(4*sqrt((s*(s-a)*(s-b)*(s-c))));
circle=2*pi*radius;
printf("%.2lf\n",circle);
}
return 0;
}
 
			  
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