https://liveyourmaths.com/international-mathematical-olympiad-2016-%cf%84%ce%b1-%ce%b8%ce%ad%ce%bc%ce%b1%cf%84%ce%b1-%cf%84%ce%b7%cf%82-1%ce%b7%cf%82-%ce%ba%ce%b1%ce%b9-2%ce%b7%cf%82-%ce%b7%ce%bc%ce%ad%cf%81%ce%b1%cf%82/