J, 0 additions, 14 bytes
Inspired by Alexei Kopylov's answer.
f=:[{]#i.@>:@[Uses no maths at all:
f=: NB. define function f [ NB. take left argument,>:@ NB. increment it, i.@ NB. generate the list [0..left arg+1) ]# NB. replicate each item in the list by the right argument NB. (so if ]=2, list becomes 0 0 1 1 2 2 3 3 ...) [{ NB. select the ['th item from that list.