What is the song that has been number one the longest?
{'directed': True, 'multigraph': False, 'graph': {}, 'nodes': [{'type': 'QUESTIONS_ENTITY', 'name_': 'Q7366', 'id': 0, 'label': 'song'}, {'type': 'INTERNAL', 'name_': 'Q27939', 'id': 1, 'label': 'singing'}, {'type': 'ANSWER_CANDIDATE_ENTITY', 'name_': 'Q685884', 'id': 2, 'label': 'vocal music'}, {'type': 'INTERNAL', 'name_': 'Q373899', 'id': 3, 'label': 'record chart'}, {'type': 'INTERNAL', 'name_': 'Q2291', 'id': 4, 'label': 'Totò'}, {'type': 'QUESTIONS_ENTITY', 'name_': 'Q20878491', 'id': 5, 'label': 'number-one hit'}, {'type': 'INTERNAL', 'name_': 'Q46919382', 'id': 6, 'label': 'Hymn to Nemesis'}], 'links': [{'name_': 'P1536', 'source': 1, 'target': 2, 'label': 'immediate cause of'}, {'name_': 'P1687', 'source': 3, 'target': 4, 'label': 'Wikidata property'}, {'name_': 'P527', 'source': 3, 'target': 5, 'label': 'has part(s)'}, {'name_': 'P101', 'source': 4, 'target': 1, 'label': 'field of work'}, {'name_': 'P7937', 'source': 6, 'target': 0, 'label': 'form of creative work'}, {'name_': 'P136', 'source': 6, 'target': 2, 'label': 'genre'}]}