Shostakovich's "Dance of the Dolls" is a suite of easy piano pieces from his Ballet Suites, which were themselves compilations of excerpts from his ballets, film scores, and incidental music. The fourth piece of the collection, called Polka, refers to the Czech folk dance. It's a lively piece, played with a sharp staccato. The central section speeds up and keeping your wrist relaxed while playing fast chords can be a real challenge.