Question: who were the leaders of the following countries during the cuban missile crisis united states
[{'answer': 'U.S. President John F. Kennedy', 'provenance': [{'wikipedia_id': '6827', 'title': 'Cuban Missile Crisis', 'start_paragraph_id': 4, 'start_character': 75, 'end_paragraph_id': 4, 'end_character': 103, 'bleu_score': 0.668740304976422, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6827', 'title': 'Cuban Missile Crisis', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 581, 'bleu_score': 0.93972795698899, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16181895462673967396}, 'section': 'Section::::Abstract.'}]}]