class Triangle {

    public double area() {
        double area = -1;
        double ab = this.a.distanceTo(this.b);
        double ac = this.a.distanceTo(this.c);
        double bc = this.b.distanceTo(this.c);
        double p = this.period(ab, ac, bc);
        if (this.exist(ab, ac, bc)) {
            area = Math.sqrt(p * (p - ab) * (p - ac) * (p - bc));
        }
        return area;
    }

    public  Triangle(Point a, Point b, Point c);

}