Task: Question Answering
Input (English): Passage: Stalin's death in 1953 was the biggest step toward Shostakovich's rehabilitation as a creative artist, which was marked by his Tenth Symphony. It features a number of musical quotations and codes (notably the DSCH and Elmira motifs, Elmira Nazirova being a pianist and composer who had studied under Shostakovich in the year before his dismissal from the Moscow Conservatory), the meaning of which is still debated, while the savage second movement, according to Testimony, is intended as a musical portrait of Stalin. The Tenth ranks alongside the Fifth and Seventh as one of Shostakovich's most popular works. 1953 also saw a stream of premieres of the "desk drawer" works.
During the forties and fifties, Shostakovich had close relationships with two of his pupils, Galina Ustvolskaya and Elmira Nazirova. In the background to all this remained Shostakovich's first, open marriage to Nina Varzar until her death in 1954. He taught Ustvolskaya from 1937 to 1947. The nature of their relationship is far from clear: Mstislav Rostropovich described it as "tender". Ustvolskaya rejected a proposal of marriage from him after Nina's death. Shostakovich's daughter, Galina, recalled her father consulting her and Maxim about the possibility of Ustvolskaya becoming their stepmother. Ustvolskaya's friend Viktor Suslin said that she had been "deeply disappointed" in Shostakovich by the time of her graduation in 1947. The relationship with Nazirova seems to have been one-sided, expressed largely through his letters to her, and can be dated to around 1953 to 1956. He married his second wife, Komsomol activist Margarita Kainova, in 1956; the couple proved ill-matched, and divorced three years later.
In 1954, Shostakovich wrote the Festive Overture, opus 96; it was used as the theme music for the 1980 Summer Olympics. (His '"Theme from the film Pirogov, Opus 76a: Finale" was played as the cauldron was lit at the 2004 Summer Olympics in Athens, Greece.)
In 1959, Shostakovich appeared on stage in Moscow at the end of a concert performance of his Fifth Symphony, congratulating Leonard Bernstein and the New York Philharmonic Orchestra for their performance (part of a concert tour of the Soviet Union). Later that year, Bernstein and the New York Philharmonic recorded the symphony in Boston for Columbia Records. 
Question: What is the last name of the man that the composer who married Margarita Kainova congratulate on stage in Moscow in 1959?
Output (English): Bernstein.