const
  maxQueue = 600;
type
  Queueitem = record dad, son : sector; end;
  Queue = record
            front, rear : 0..maxQueue;
            data        : array [1..maxQueue] of Queueitem;
          end;

procedure serve( var q : queue; var e1, e2 : sector );
begin
  if q.front = 0 then
    writeln('serving from an empty queue!')
  else
    begin
      e1 := q.data[ q.front ].dad;
      e2 := q.data[ q.front ].son;
      if q.front = maxQueue then
        q.front := 1
      else
        q.front := q.front + 1;
      if q.front = q.rear then  { empty queue }
        q.front := 0;
    end; {else}
end; {serve}

procedure enqueue( var q : queue; e1, e2 : sector );
begin
  if q.front = 0 then
    begin
      q.front := 1;
      q.rear := 2;
      q.data[1].dad:= e1;
      q.data[1].son := e2;
    end {if}
  else if q.front = q.rear then
    writeln('queue full!')
  else
    begin
      q.data[ q.rear ].dad := e1;
      q.data[ q.rear].son := e2;
      if q.rear = maxQueue then
        q.rear := 1
      else
        q.rear := q.rear + 1;
    end; {else}
end; {enqueue}