#include<iostream>
#include<cmath>
using namespace std;
#define pi 3.141592653589793
int main()
{
	double x1,y1,x2,y2,x3,y3,a,b,c,l,s,r,L;
	while(cin>>x1>>y1>>x2>>y2>>x3>>y3)
	{
		a=sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
		b=sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));
		c=sqrt((x2-x3)*(x2-x3)+(y2-y3)*(y2-y3));
		l=(a+b+c)/2;
		s=sqrt(l*(l-a)*(l-b)*(l-c));
		r=(a*b*c)/(4*s);
		L=2*pi*r;
		printf("%.2f\n",L);
	}
	return 0;
}

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