Now that i think about it, i wonder same in life as well.
1967B1 - Переворотная карта (простая версия)
if a+b ⋮ b*gcd(a,b) then a ⋮ b*gcd(a,b) so gcd(a,b) is b therefor a⋮b^2
p.s i didn't get the editorial so someone telling me it would be nice as well