Question: what is the second series of percy jackson called
[{'answer': 'The Heroes of Olympus', 'provenance': [{'wikipedia_id': '28056365', 'title': 'The Heroes of Olympus', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '28056365', 'title': 'The Heroes of Olympus', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 585, 'bleu_score': 0.6430088193301311, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1350919196439331564}, 'section': 'Section::::Abstract.'}]}]