What is wrong with this code


program Project4;
{$APPTYPE CONSOLE}

{$M 16777216}

uses
  Math;

type
  Pt = record
    x, y: integer;
  end;
  float = Extended;

function left(const p1, p2, p3: Pt): boolean; inline;
begin
  Result := ((p2.x - p1.x) * (p3.y - p1.y) - (p2.y - p1.y) * (p3.x - p1.x)) > 0;
end;

function dist(const p1, p2: Pt): float; inline;
begin
  Result := Sqrt(Sqr(p1.x - p2.x) + Sqr(p1.y - p2.y));
end;

var
  ans: float;
  i, n, l, j: integer;
  p, s: array[1..1001] of Pt;
  pointOnHull, endPoint: Pt;

begin
  Readln(n, l);
  pointOnHull.x := 1000001;
  pointOnHull.y := 1000001;
  for i := 1 to n do
  begin
    Readln(p[i].x, p[i].y);
    if (p[i].x < pointOnHull.x) then
    begin
      pointOnHull := p[i];
    end
    else
    if ((p[i].x = pointOnHull.x) and (p[i].y < pointOnHull.y)) then
    begin
      pointOnHull := p[i];
    end;
  end;
  j := 1;
  repeat
    s[j] := pointOnHull;
    endPoint := p[1];
    for i := 2 to n do
    begin
      if (((endpoint.x = pointOnHull.x) and (endpoint.y = pointOnHull.y)) or (left(p[i], pointOnHull, endpoint))) then
      begin
        endpoint := p[i];
      end;
    end;
    Inc(j);
    pointOnHull := endPoint;
  until (endPoint.x = s[1].x) and (endPoint.y = s[1].y);
  ans := dist(s[1], s[j - 1]);
  for i := 2 to j - 1 do
  begin
    ans := ans + dist(s[i], s[i - 1]);
  end;
  ans := Round(ans + 2 * PI * l);
  Writeln(ans:0:0);
  {$IFNDEF ONLINE_JUDGE}
  Readln;
  {$ENDIF}
end.


This uses 'gift-wrapping' algorithm described in http://en.wikipedia.org/wiki/Gift_wrapping_algorithm
but it can't pass test 12.
As you can see, I use 'extended', so it is not problem of precision.

Edited by author 01.04.2013 19:45

Edited by author 01.04.2013 19:47