3A : Площадь треугольника

program _3A;

type
  Point = record
    x, y : Int64;
  end;

var
  a, b, c, ab, ac : Point;
  s : Int64;

begin
  ReadLn(a.x, a.y);
  ReadLn(b.x, b.y);
  ReadLn(c.x, c.y);
  ab.x := b.x - a.x;
  ab.y := b.y - a.y;
  ac.x := c.x - a.x;
  ac.y := c.y - a.y;
  s := ab.x * ac.y - ab.y * ac.x;
  s := abs(s);
  WriteLn(s / 2);
end.