using System;

public class Program

{

    public static void Main()

    {

        var x1 = int.Parse(Console.ReadLine());

        var y1 = int.Parse(Console.ReadLine());

        var x2 = int.Parse(Console.ReadLine());

        var y2 = int.Parse(Console.ReadLine());

        var x3 = int.Parse(Console.ReadLine());

        var y3 = int.Parse(Console.ReadLine());

        int biggerX = x1;

        if (x2 > biggerX) 

        {

            biggerX = x2;

        }

        if (x3 > biggerX)

        {

            biggerX = x3;

        }

        int smallerX = x1;

        if (x2 < smallerX)

        {

            smallerX = x2;

        }

        if (x3 < smallerX)

        {

            smallerX = x3;  

        }

        int biggerY = y1;

        if (y2 > biggerY) 

        {

            biggerY = y2;

        }

        if (y3 > biggerY)

        {

            biggerY = y3;

        }

        int smallerY = y1;

        if (y2 < smallerY)

        {

            smallerY = y2;

        }

        if (y3 < smallerY)

        {

            smallerY = y3;  

        }

        int rectangleWrapperArea = (biggerX - smallerX) * (biggerY - smallerY);

        double rectangleArea1 = (Math.Abs(x1 - x2) * Math.Abs(y1 - y2)) / 2.0;

        double rectangleArea2 = (Math.Abs(x2 - x3) * Math.Abs(y2 - y3)) / 2.0;

        double rectangleArea3 = (Math.Abs(x1 - x3) * Math.Abs(y1 - y3)) / 2.0;

        double rectangleArea = rectangleWrapperArea - (rectangleArea1 + rectangleArea2 + rectangleArea3);

        Console.WriteLine(rectangleArea);

​

    }

}