Instructions: In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.
Input: Passage: Inside the SAPD, the first part of 1937 saw an intensification of differences over attitudes to a possible political party of the united left or a Popular front, and more precisely over the party's approach to the Soviet Union. The differences led to Peter Blachstein's exclusion from the SAPD. Others excluded at the same time included his political mentor and Erwin Ackerknecht: the three became the focus of a short-lived political grouping known as "Neuer Weg" ("New Way"). Blachstein was also affected more directly by the intense political tensions radiating out from Moscow, based on Stalin's suspicions - not entirely unfounded - that there might be comrades in the Soviet Union and further west in Europe who favoured an alternative Soviet leader. The POUM, of which Blachstein was a member, backed a broadly Trotskyite vision for a communist future and its members therefore became targets for Soviet agents. In June 1937 Blachstein was arrested in Barcelona by communist secret police and accused of spying for Franco and working for the Gestapo. With approximately 100 other foreign detainees he was taken to a large garage which had been adapted for use as an ad hoc prison. Because of the appalling hygiene he soon fell ill with Tuberculosis, as a result of which he was transferred to a sanatorium controlled by anarchist comrades. Helped by Spanish friends, in January 1938 he succeeded in escaping back to France.
 Link Information: Lenin died in January 1924. Stalin took charge Question: How long had Stalin been the leader of the Soviet Union by the year 1937?
Output:
Answer: 13