using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Triangle_Area
{
    class Program
    {
        static void Main(string[] args)
        {
            double x1 = double.Parse(Console.ReadLine());
            double y1 = double.Parse(Console.ReadLine());
            double x2 = double.Parse(Console.ReadLine());
            double y2 = double.Parse(Console.ReadLine());
            double x3 = double.Parse(Console.ReadLine());
            double y3 = double.Parse(Console.ReadLine());

            double a = Math.Abs(x2 - x3);
            double h = Math.Abs(y1 - y2);

            Console.WriteLine(a * h / 2);
        }
    }
}