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 15 (2021)
    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.