1.

/**
* ACM Training 2009
* ACM Problem #438 - Circumference of a circle
* Link: http://uva.onlinejudge.org/external/4/438.html
*
* @author Felix Dietrich
* @version 1.0, 09/21/2009
*
* Methode: Geometry, midpoints
* Status : Accepted
* Runtime: 0.196
*/

import java.util.Locale;
import java.util.Scanner;

public class Main
{
public static void main(String... s)
{
Scanner sc = new Scanner(System.in);

sc.useLocale(Locale.ENGLISH);

double a[] = new double[2];
double b[] = new double[2];
double c[] = new double[2];
double pi = 3.141592653589793;

while(sc.hasNext())
{
a[0] = sc.nextDouble();
a[1] = sc.nextDouble();
b[0] = sc.nextDouble();
b[1] = sc.nextDouble();
c[0] = sc.nextDouble();
c[1] = sc.nextDouble();

System.out.println(String.format("%.02f", 2.0*pi*rad(a,b,c)));
}
}

private static double rad(double[] b, double[] c, double[] d)
{
double temp = c[0]*c[0]+c[1]*c[1];
double bc = (b[0]*b[0] + b[1]*b[1] - temp)/2.0;
double cd = (temp - d[0]*d[0] - d[1]*d[1])/2.0;
double det = (b[0]-c[0])*(c[1]-d[1])-(c[0]-d[0])*(b[1]-c[1]);
/*if (Math.abs(det) < 1.0e-6)
{
c->center.xw = c->center.yw = 1.0;
c->center.w = 0.0;
c->v1 = *v1;
c->v2 = *v2;
c->v3 = *v3;
return;
}*/
det = 1.0/det;
double centerx = (bc*(c[1]-d[1])-cd*(b[1]-c[1]))*det;
double centery = ((b[0]-c[0])*cd-(c[0]-d[0])*bc)*det;
return Math.sqrt((centerx-b[0])*(centerx-b[0])+(centery-b[1])*(centery-b[1]));
}
}