This piano music is the Prelude in C-sharp minor by Sergei Rachmaninoff. This was first published as the 2nd movement in the composer's "Morceaux de Fantaisie" (Fantasy Pieces) Op.3. It appears that Rachmaninoff later decided to write a total of 24 preludes, one in each major and minor key, just as other composers had done. Maybe the instant popularity of the Prelude helped to convince him. (One of the other 24 preludes is the G-minor and a link to this piece is in the left-hand menu.) The C-sharp minor prelude has a fast middle section, and when the slow section returns, not only is it marked sfff and then sffff to indicate very loudly accented, but each of the pianist's two hands are spread over two staves for clarity. Below is a video of the sheet music being played in Sibelius, or scroll down to play the mp3 file and see the sheet music PDF. You can download this sheet music in PDF format, and the corresponding midi and mp3 files using the links in the left-hand menu.