Question: when did the us flag change from 13 stars
[{'answer': 'April 4 , 1818', 'provenance': [{'wikipedia_id': '11447', 'title': 'Flag of the United States', 'start_paragraph_id': 22, 'start_character': 3, 'end_paragraph_id': 22, 'end_character': 17, 'bleu_score': 1.0, 'section': 'Section::::History.:Later flag acts.\n'}]}, {'provenance': [{'wikipedia_id': '11447', 'title': 'Flag of the United States', 'start_paragraph_id': 22, 'start_character': 0, 'end_paragraph_id': 22, 'end_character': 694, 'bleu_score': 0.9632888883202131, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7969662715730003182}, 'section': 'Section::::History.:Later flag acts.\n'}]}]