1. 

/**
* Angewandte Mathematik, SS09, IFB 2C
* ACM Problem 438 - The Circumference of the Circle
* Link: http://icpcres.ecs.baylor.edu/onlinejudge/index.php?option=com_onlinejudge&Itemid=8&category=6&page=show_problem&problem=379
* @author Miesel Christoph
* @author Seilbeck Robert
* @author Wolfram Andre
* @version 2.0 04.05.2009
*
* Status : Accepted
* Runtime: 0.130
*/

import java.io.*;
import java.util.*;
public class Umfang
{
public static void main(String[] args)throws Exception
{
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String line = reader.readLine();

while(line != null)
{
StringTokenizer t = new StringTokenizer(line);
double x1 = 1;
double y1 = 1;
double x2 = 1;
double y2 = 1;
double x3 = 1;
double y3 = 1;
while(t.hasMoreTokens())
{
x1 = Double.parseDouble(t.nextToken());
y1 = Double.parseDouble(t.nextToken());
x2 = Double.parseDouble(t.nextToken());
y2 = Double.parseDouble(t.nextToken());
x3 = Double.parseDouble(t.nextToken());
y3 = Double.parseDouble(t.nextToken());

}
double schlapprigerUmfang;
schlapprigerUmfang = 3.141592653589793*Math.sqrt(Math.pow(x2-x1,2)+Math.pow(y2-y1,2))*Math.sqrt(Math.pow(x3-x1, 2)+Math.pow(y3-y1, 2))*Math.sqrt(Math.pow(x3-x2, 2)+Math.pow(y3-y2, 2))/((x2-x1)*(y3-y1)-(y2-y1)*(x3-x1));
if(schlapprigerUmfang<0)
schlapprigerUmfang*=-1;
System.out.println(((double)Math.round(schlapprigerUmfang*100)/100)+"");
line = reader.readLine();
}

}
}

2.


/**
* Angewandte Mathematik, SS09, IFB 2C
* ACM Problem: The Circumference of the Circle (438)
* @author Christian Mitterreiter
* @author Rolf Luigs
* @version 1.0, 05/03/2009
* Status : Accepted
* Runtime: 0.160
*/


import java.util.Scanner;

public class Main {

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

while(sc.hasNextDouble()) {
double x1 = sc.nextDouble();
double y1 = sc.nextDouble();
double x2 = sc.nextDouble();
double y2 = sc.nextDouble();
double x3 = sc.nextDouble();
double y3 = sc.nextDouble();


double U = 0;

double U_zaehler = Math.sqrt(Math.pow(x2-x1,2)+Math.pow(y2-y1,2))*Math.sqrt(Math.pow(x3-x1,2)+Math.pow(y3-y1,2))*Math.sqrt(Math.pow(x3-x2, 2)+Math.pow(y3-y2, 2));
double U_nenner = ((x2-x1)*(y3-y1))-((y2-y1)*(x3-x1));

U = Math.abs(Math.PI*(U_zaehler/U_nenner));

System.out.printf("%.2f\n",U);

}
}
}