Question: who has been number 1 in tennis the longest
[{'answer': 'Roger Federer', 'provenance': [{'wikipedia_id': '2575118', 'title': 'List of ATP number 1 ranked singles tennis players', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 13, 'bleu_score': 1.0, 'section': 'Section::::Records and particularities.\n'}]}]