#include <iostream>
#include <math.h>

using namespace std;

const float pi = 3.14159265358979323846;

struct point{
	static point from_stdin(){
		point p;
		cin >> p.x >> p.y;
		return p;		
	} 
	float dist(point &r) {	
		float dx = x - r.x;
		float dy = y - r.y;
		return sqrtf(dx*dx + dy*dy);
	}	
	float x, y;
};

float areaCircle(point p, point r) {
	float rad = p.dist(r)/2;
	return pi*rad*rad;
}

int main()
{
	point a = point::from_stdin();
	point b = point::from_stdin();
	point c = point::from_stdin();
	
	float tri = a.dist(b) * a.dist(c) / 2;
	float circA = areaCircle(a, b)/2;
	float circB = areaCircle(a, c)/2;
	float circC = areaCircle(b, c)/2;
	
	cout << tri + circA + circB - circC << endl;
	return 0;
}