begin
  i:=1;
  min:=x[0];
  max:=x[0];
  m1:=0;
  m3:=0;
  repeat
    if x[i]<min
    then
    begin
      min:=x[i];
      m1:=i;
    end
    else
    begin
      if x[i]>max
      then
      begin
        max:=x[i];
        m3:=i;
      end;
    end;
    i:=i+1;
  until not(i<=n);
  R :=-MaxReal;
  i:=0;
  repeat
    if x[i]<>x[m1]
    then
    begin
      t:=(y[i]-y[m1])/(x[i]-x[m1]);
      if t>r
      then
      begin
        m2:=i;
        r:=t;
      end;
    end;
    i:=i+1
  until not(i<=n);
  x[n+1]:=x[m1]+x[m2]-x[m3];
  y[n+1]:=y[m1]+y[m2]-y[m3];
  nt:=-1;
  Top:=1;
  Stack[1,Top]:=m1;
  Stack[2,Top]:=m2;
  Stack[3,Top]:=n+1;
  while Top<>0 do
  begin
    p1:=Stack[1,Top];
    p2:=Stack[2,Top];
    p3:=Stack[3,Top];
    Top:=Top-1;
    m:=-1;
    r1:=MaxReal;
    i:=0;
    repeat
      c:=not(IOS(x[p3],y[p3],x[i],y[i],x[p1],y[p1],x[p2],y[p2]));
      if (i<>p1)and(i<>p2)
      and C
      then
      begin
        roi1:=Sqrt(Sqr(x[i]-x[p1])+Sqr(y[i]-y[p1]));
        roi2:=Sqrt(Sqr(x[i]-x[p2])+Sqr(y[i]-y[p2]));
        r:=((x[p1]-x[i])*(x[p2]-x[i])+(y[p1]-y[i])*(y[p2]-y[i]))/roi1/roi2;
        if r<r1
        then
        begin
          r1:=r;
          m:=i;
        end;
      end;
      i:=i+1
    until not(i<=n);
    if (M>=0)and(p3<>M)
    then
    begin
      i:=0;
      et:=False;
      while (i<=nt) and not(et) do
      begin
        ET:=((p1=tr[1,i])and(p2=tr[2,i])and(m=tr[3,i]))
        or((p1=tr[1,i])and(p2=tr[3,i])and(m=tr[2,i]))
        or((p1=tr[2,i])and(p2=tr[1,i])and(m=tr[3,i]))
        or((p1=tr[2,i])and(p2=tr[3,i])and(m=tr[1,i]))
        or((p1=tr[3,i])and(p2=tr[1,i])and(m=tr[2,i]))
        or((p1=tr[3,i])and(p2=tr[2,i])and(m=tr[1,i]));
        i:=i+1;
      end;
      if not(et)
      then
      begin
        nt:=nt+1;
        tr[1,nt]:=p1;
        tr[2,nt]:=p2;
        tr[3,nt]:=m;
        Top:=Top+1;
        Stack[1,Top]:=p1;
        Stack[2,Top]:=m;
        Stack[3,Top]:=p2;
        Top:=Top+1;
        Stack[1,Top]:=p2;
        Stack[2,Top]:=m;
        Stack[3,Top]:=p1;
      end;
    end;
  end;
end;