Apex domains cannot have CNAME records.
Question and response
Question
dig cloud4box.ru. NS
Answer
cloud4box.ru. 5 NS ns2.contell.ru.
cloud4box.ru. 5 NS ns1.contell.ru.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0