How many books are in Stieg Larsson's Millennium novel series?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'QUESTIONS_ENTITY', 'name_': 'Q186317', 'id': 0, 'label': 'Stieg Larsson'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q847022', 'id': 1, 'label': 'Millennium'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q1137369', 'id': 2, 'label': 'The Girl Who Played with Fire'}], 'links': [{'name_': 'P50', 'source': 2, 'target': 0, 'label': 'author'}, {'name_': 'P179', 'source': 2, 'target': 1, 'label': 'part of the series'}]}