TriangleArea

import java.util.Scanner;

public class TriangleArea {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int[] points = new int[6];
        double[] lengths = new double[3];
        for(int i = 0; i < 3; i++) {
            System.out.print("Enter coords of point " + (char)('A' + i) + ": ");
            points[i * 2] = sc.nextInt();
            points[i * 2 + 1] = sc.nextInt();
            System.out.println();
        }
        for (int i = 0; i < 2; i++) {
            lengths[i] = getLength(points[i * 2], points[i * 2 + 1],
                                  points[(i + 1) * 2], points[(i + 1) * 2 + 1]);
        }
        lengths[2] = getLength(points[0], points[1], points[4], points[5]);

        if(isTrianlge(lengths)) {
            System.out.println(Math.round(heronArea(lengths)));
        }
        else {
            System.out.println(0);
        }

    }

    private static double heronArea(double[] lengths) {
        double perimeter = lengths[0] + lengths[1] + lengths[2];
        double semiperimeter = perimeter / 2;
        double area = Math.sqrt( semiperimeter *
                                 (semiperimeter - lengths[0]) *
                                 (semiperimeter - lengths[1]) *
                                 (semiperimeter - lengths[2]) );
        return area;
    }

    private static boolean isTrianlge(double[] lengths) {
        boolean isTriangle;
        isTriangle = (lengths[0] < lengths[1] + lengths[2]
                      || lengths[1] < lengths[0] + lengths[2]
                      || lengths[2] < lengths[0] + lengths[1]);
        return isTriangle;
    }

    private static double getLength(int firstPointX, int firstPointY, int secondPointX, int secondPointY) {
        double length = Math.sqrt((firstPointX - secondPointX) * (firstPointX - secondPointX)
                                + (firstPointY - secondPointY) * (firstPointY - secondPointY));
        return length;
    }
}