Task: Question Understanding
Input (English): Passage: On 18 February 1921, the ARF led an anti-Soviet rebellion in Yerevan and seized power. The ARF controlled Yerevan and the surrounding regions for almost 42 days before being defeated by the numerically superior Red Army troops later in April 1921. The leaders of the rebellion then retreated into the Syunik region. On 26 April 1921, the 2nd Pan-Zangezurian congress, held in Tatev monastery, announced the independence of the self-governing regions of Daralakyaz , Zangezur, and Mountainous Artsakh, under the name of the Republic of Mountainous Armenia and later on 1 June 1921, it was renamed the Republic of Armenia.
Question: On what date did the ARF stop controlling Yerevan?
Output (English): date