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

using namespace std;

const double pi = 3.14159265358979323846;

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

double areaCircle(point p, point r) {
	double 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();
	
	double tri = a.dist(b) * a.dist(c) / 2;
	
	cout << fixed << setprecision(9) << tri << endl;
	return 0;
}