Schubert's Impromptu D. 899 No. 1 is a dramatic and lyrical piece characterized by its C minor tonality and march-like rhythmic drive. The work is notable for its lack of a traditional key signature and its expansive, developmental structure.
Managing the rhythmic precision of the opening march and the voicing of the inner melodic lines is essential.
Adieu! is rated Henle level 3 of 9 — late beginner repertoire, roughly ABRSM grades 4–5. In the RCM system it corresponds to about level 7.
You should be comfortable at Henle level 3 — meaning you can already play level 2–3 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Adieu! lasts about 5 minutes.
Adieu! is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.