Apex domains cannot have CNAME records.
Question and response
Question
dig DENSKY.RU. NS
Answer
densky.ru. 4 NS ns.obtelecom.ru.
densky.ru. 4 NS ns.densky.ru.
Authority
The response has no authority records.
Additional
ns.DENSKY.RU. 4 A 195.88.17.246
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0