The journal titled "OLYMPIADS IN INFORMATICS" is published every year, starting with 2007. Only original high-quality scientific papers are part of the journal, and they are all free to access.

You can click on an edition to read it:
    pdf  index  Volume 14 (2020)
    pdf  index  Volume 13 (2019)
    pdf  index  Volume 12 (2018)
    pdf  index  Volume 11 (2017)
    pdf  index  Volume 10 (2016)
    pdf  index  Volume  9 (2015)
    pdf  index  Volume  8 (2014)
    pdf  index  Volume  7 (2013)
    pdf  index  Volume  6 (2012)
    pdf  index  Volume  5 (2011)
    pdf  index  Volume  4 (2010)
    pdf  index  Volume  3 (2009)
    pdf  index  Volume  2 (2008)
    pdf  index  Volume  1 (2007)

A couple of special editions have also been published:
    pdf  index  Volume 11 - Special Edition (2017)
    pdf  index  Volume 10 - Special Edition (2016)

The content links above contain the journal volumes.
Alternatively, you can find an index of all papers as separate files here.