Task: Question Answering
Input (English): Passage: After graduation, Shostakovich initially embarked on a dual career as concert pianist and composer, but his dry style of playing was often unappreciated (his American biographer, Laurel Fay, comments on his "emotional restraint" and "riveting rhythmic drive"). He nevertheless won an "honorable mention" at the First International Chopin Piano Competition in Warsaw in 1927. He attributed the disappointment at the competition to suffering from appendicitis and the jury being all-Polish. He had his appendix removed in April 1927. After the competition Shostakovich met the conductor Bruno Walter, who was so impressed by the composer's First Symphony that he conducted it at its Berlin premiere later that year. Leopold Stokowski was equally impressed and gave the work its U.S. premiere the following year in Philadelphia and also made the work's first recording.
Shostakovich concentrated on composition thereafter and soon limited his performances primarily to those of his own works. In 1927 he wrote his Second Symphony (subtitled To October), a patriotic piece with a great pro-Soviet choral finale. Owing to its experimental nature, as with the subsequent Third Symphony, it was not critically acclaimed with the enthusiasm given to the First.
1927 also marked the beginning of Shostakovich's relationship with Ivan Sollertinsky, who remained his closest friend until the latter's death in 1944. Sollertinsky introduced the composer to the music of Mahler, which had a strong influence on his music from the Fourth Symphony onwards.
While writing the Second Symphony, Shostakovich also began work on his satirical opera The Nose, based on the story by Nikolai Gogol. In June 1929, against the composer's own wishes, the opera was given a concert performance; it was ferociously attacked by the Russian Association of Proletarian Musicians (RAPM). Its stage premiere on 18 January 1930 opened to generally poor reviews and widespread incomprehension among musicians.In the late 1920s and early 1930s, Shostakovich worked at TRAM, a proletarian youth theatre. Although he did little work in this post, it shielded him from ideological attack. Much of this period was spent writing his opera, Lady Macbeth of the Mtsensk District, which was first performed in 1934. It was immediately successful, on both popular and official levels. It was described as "the result of the general success of Socialist construction, of the correct policy of the Party", and as an opera that "could have been written only by a Soviet composer brought up in the best tradition of Soviet culture".Shostakovich married his first wife, Nina Varzar, in 1932. Initial difficulties led to a divorce in 1935, but the couple soon remarried when Nina became pregnant with their first child, Galina. 
Question: What is the name of the composer who was introduced to the music of Mahler by Sollertinsky?
Output (English): Shostakovich.