Apex domains cannot have CNAME records.
Question and response
Question
dig sweb.ru. NS
Answer
sweb.ru. 5 NS ns2.sweb.ru.
sweb.ru. 5 NS ns4.sweb.ru.
sweb.ru. 5 NS ns1.sweb.ru.
Authority
The response has no authority records.
Additional
ns1.sweb.ru. 5 A 31.177.67.100
ns2.sweb.ru. 5 A 31.177.74.100
ns4.sweb.ru. 5 A 31.177.85.186
ns1.sweb.ru. 5 AAAA 2a02:2090:e800:9000:31:177:67:100
ns2.sweb.ru. 5 AAAA 2a02:2090:ec00:9040:31:177:74:100
ns4.sweb.ru. 5 AAAA 2a02:2090:e400:7000:31:177:85:186
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0