Question: when did lionel messi started playing for barcelona
[{'answer': '2001', 'provenance': [{'wikipedia_id': '2150841', 'title': 'Lionel Messi', 'start_paragraph_id': 8, 'start_character': 487, 'end_paragraph_id': 8, 'end_character': 491, 'bleu_score': 1.0, 'section': 'Section::::Early life.\n'}]}]