#include <iostream>
#include <cmath>

using namespace std;

int main()
{

    int x1,y1,x2,y2,x3,y3;
    double a,b,c,s,p,r;
    cin >>x1>>y1>>x2>>y2>>x3>>y3;
    a = sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1));
    b = sqrt((x3-x2)*(x3-x2)+(y3-y2)*(y3-y2));
    c = sqrt((x3-x1)*(x3-x1)+(y3-y1)*(y3-y1));
    p =(a + b + c)/2;
    s = sqrt(p * (p - a) * (p - b) * (p - c));
    r = (a*b*c)/(4*s);
    cout.setf(ios::fixed | ios::showpoint);
    cout.precision(3);
    if(s == 0)
    {
        cout << 3.141592653589793238462643383279 *(max(max(a,b),max(a,c))) <<endl;
        return 0;
    }
    cout << 2 * 3.141592653589793238462643383279 * r << endl;
    return 0;
}