Nocturne in C minor, Op. posth. (Chopin)

Frédéric Chopin's Nocturne No. 21 in C minor, B. 108 is a musical work for solo piano composed in 1837. It was the last of Chopin's nocturnes to be published, and was done so posthumously in 1938. It is famous for its striking simplicity and folk-like melody. Among the 21 nocturnes known to have been written by Chopin, this is one of the three that end in a minor key - the other two being No. 13 in C Minor and No. 9 in B Major. 
Structure.
The composition is structured as a single movement marked: "Andante sostenuto"