P2 Call Stack

program P2(output);
  var A: integer;
  procedure S (procedure
      T(var X: integer)); forward;
  procedure Q (var B: integer);
    var C: integer;
    begin
      C := B + A;
      writeln(C);
      if B > 0 then S(Q)
    end;
  procedure S;
    var C: integer;
    begin
      C := 0;
      T(C)
    end;
  begin
    A := 7;
    Q(A)
  end.