import java.util.Scanner;


public class _02_TriangleArea {
    public static void main(String[] args) {
        @SuppressWarnings("resource")
        Scanner input = new Scanner(System.in);
        int aX = input.nextInt();
        int aY = input.nextInt();
        int bX = input.nextInt();
        int bY = input.nextInt();
        int cX = input.nextInt();
        int cY = input.nextInt();
        int area = (aX * (bY - cY) + bX * (cY - aY) + cX * (aY - bY)) / 2;
        System.out.println(Math.abs(area));
    }
}