if ($('amount_other') && $('custom_34')) {

  function update_six_flags_2009() {
    if($('custom_34').value=="") $('custom_34').value = '0';
    $('amount_other').value = ( isNaN($('custom_34').value) ? 0 : parseInt($('custom_34').value) * 27);
		$('amount_other').readOnly = true;
  }

  $('custom_34').addEvent(    'change', function() {update_six_flags_2009();} );
  $('amount_other').addEvent( 'change', function() {update_six_flags_2009();} );
  update_six_flags_2009();
}