Question: what's the population of walnut grove minnesota
[{'answer': '871', 'provenance': [{'wikipedia_id': '121519', 'title': 'Walnut Grove, Minnesota', 'start_paragraph_id': 1, 'start_character': 87, 'end_paragraph_id': 1, 'end_character': 90, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]