Question: who was the leader of the soviet union when the berlin wall was built
[{'answer': 'Khrushchev', 'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 34, 'start_character': 50, 'end_paragraph_id': 34, 'end_character': 60, 'bleu_score': 1.0, 'section': 'Section::::Construction begins, 1961.\n'}]}, {'answer': 'Joseph Stalin', 'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 10, 'start_character': 38, 'end_paragraph_id': 10, 'end_character': 51, 'bleu_score': 1.0, 'section': 'Section::::Background.:Eastern Bloc and the Berlin airlift.\n'}]}, {'answer': 'Nikita Khrushchev', 'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 34, 'start_character': 43, 'end_paragraph_id': 34, 'end_character': 60, 'bleu_score': 1.0, 'section': 'Section::::Construction begins, 1961.\n'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10152493754205718463}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 35, 'start_character': 0, 'end_paragraph_id': 35, 'end_character': 681, 'bleu_score': 0.684945361068772, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10152493754205718463}, 'section': 'Section::::Construction begins, 1961.\n'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 10, 'start_character': 0, 'end_paragraph_id': 10, 'end_character': 556, 'bleu_score': 0.977897140678983, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10152493754205718463}, 'section': 'Section::::Background.:Eastern Bloc and the Berlin airlift.\n'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'start_paragraph_id': 34, 'start_character': 0, 'end_paragraph_id': 34, 'end_character': 449, 'bleu_score': 0.8641242892967471, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10152493754205718463}, 'section': 'Section::::Construction begins, 1961.\n'}]}, {'provenance': [{'wikipedia_id': '3722', 'title': 'Berlin Wall', 'section': 'Section::::Construction begins, 1961.\n', 'start_paragraph_id': 34, 'end_paragraph_id': 34, 'meta': {'evidence_span': ["The transcript of a telephone call between Nikita Khrushchev and Ulbricht, on 1 August in the same year, suggests that the initiative for the construction of the Wall came from Khrushchev. However, other sources suggest that Khrushchev had initially been wary about building a wall, fearing negative Western reaction. Nevertheless, Ulbricht had pushed for a border closure for quite some time, arguing that East Germany's very existence was at stake.\rhighlight sentence(s) containing evidence, not only the answer", 'The transcript of a telephone call between Nikita Khrushchev and Ulbricht, on 1 August in the same year, suggests that the initiative for the construction of the Wall came from Khrushchev. However, other sources suggest that Khrushchev had initially been wary about building a wall, fearing negative Western reaction.', 'The transcript of a telephone call between Nikita Khrushchev and Ulbricht, on 1 August in the same year, suggests that the initiative for the construction of the Wall came from Khrushchev']}}]}, {'provenance': [{'wikipedia_id': '43356476', 'title': 'De-Stalinization', 'section': 'Section::::Terminology issues.\n', 'start_paragraph_id': 4, 'end_paragraph_id': 4, 'meta': {'evidence_span': ['1953, consisting of Georgi Malenkov, Premier of the Soviet Union; Lavrentiy Beria, head of the Ministry of the Interior; and Nikita Khrushchev, First Secretary of the Central Committee of the Communist Party of the Soviet Union (CPSU). The term "de-Stalinization" is one which gained currency in both Russia and the Western world following the collapse of the Soviet Union, and was never used during the Khrushchev era. However, de-Stalinization efforts were set forth at this time by Nikita Khrushchev and the Government of the Soviet Union under the guise of the "overcoming/exposure of the cult of personality", with a heavy criticism of Joseph Stalin\'s "era of the cult of personality". However, prior to Khrushchev\'s "Secret Speech" to the 20th Party Congress, no direct association between Stalin as a person and "the cult of personality" was openly made by Khrushchev or others within the party, although archival documents show that strong criticism of Stalin and his ideology featured in private discussions by Khruschchev at the Presidium of the Supreme Soviet.\rhighlight sentence(s) containing evidence, not only the answer', 'The term "de-Stalinization" is one which gained currency in both Russia and the Western world following the collapse of the Soviet Union, and was never used during the Khrushchev era. However, de-Stalinization efforts were set forth at this time by Nikita Khrushchev and the Government of the Soviet Union under the guise of the "overcoming/exposure of the cult of personality", with a heavy criticism of Joseph Stalin\'s "era of the cult of personality".']}}]}]