Task: Question Answering
Input (English): Passage: The Mozart children were not alone as 18th-century music prodigies. Education writer Gary Spruce refers to hundreds of similar cases, and cites that of William Crotch of Norwich who in 1778, at the age of three, was giving organ recitals. British scholar Jane O'Connor explains the 18th century fascination with prodigies as "the realisation of the potential entertainment and fiscal value of an individual child who was in some way extraordinary". Other childhood contemporaries of Mozart included the violinist and composer Thomas Linley, born the same year as Wolfgang, and the organist prodigy Joseph Siegmund Bachmann. Mozart eventually became recognised among prodigies as the future standard for early success and promise.Of seven children born to Leopold and Anna Maria Mozart, only the fourth, Maria Anna (Nannerl), born 31 July 1751, and the youngest, Wolfgang Amadeus, born 27 January 1756, survived infancy. The children were educated at home, under Leopold's guidance, learning basic skills in reading, writing, drawing and arithmetic, together with some history and geography. Their musical education was aided by exposure to the constant rehearsing and playing of Leopold and his fellow musicians. When Nannerl was seven her father began to teach her to play the harpsichord, with Wolfgang looking on; according to Nannerl's own account "the boy immediately showed his extraordinary, God-given talent. He often spent long periods at the clavier, picking out thirds, and his pleasure showed that they sounded good to him... When he was five years old he was composing little pieces which he would play to his father who would write them down". A family friend, the poet Johann Andreas Schachtner, recounted that at the age of four Wolfgang began to compose a recognisable piano concerto, and was able to demonstrate a phenomenal sense of pitch. 
Question: What is the last name of the friend of the family that only had two of seven children survive childbirth who recounted hearing Wolfgang demonstrating phenomenal pitch at age four?
Output (English): Schachtner.