Besides the length of Charles Grethen's primary race event, which two race lengths are standard in middle-distance running?
Charles Grethen: Charles Grethen (born 2 June 1992 in Tuntange) is a Luxembourgian middle-distance runner competing primarily in the 800 metres. Middle-distance running:  The standard middle distances are the 800 metres, 1500 metres and mile run, although the 3000 metres may also be classified as a middle-distance event.
i don't know