#include <iostream>
#include <math.h>
#include<stdio.h>
using namespace std;
int main(){
const double pi = 3.141592653589793;
double x1,y1,x2,y2,x3,y3,cosA;
double a,b,c;
while(scanf("%lf %lf %lf %lf %lf %lf",&x1,&y1,&x2,&y2,&x3,&y3)!=EOF)
{
a = (double)sqrt((y2-y1)*(y2-y1)+(x2-x1)*(x2-x1));
b = (double)sqrt((y3-y1)*(y3-y1)+(x3-x1)*(x3-x1));
c = (double)sqrt((y2-y3)*(y2-y3)+(x2-x3)*(x2-x3));
cosA = (b*b+c*c-a*a)/(2*b*c);
printf("%.2f\n",pi*a/sqrt(1-cosA*cosA));
}
return 0;
}
