Apex domains cannot have CNAME records.
Question and response
Question
dig NA4U.RU. NS
Answer
NA4U.RU. 5 NS ns4.netangels.RU.
NA4U.RU. 5 NS ns3.netangels.RU.
NA4U.RU. 5 NS ns1.netangels.RU.
NA4U.RU. 5 NS ns2.netangels.RU.
Authority
The response has no authority records.
Additional
ns1.netangels.RU. 5 A 91.201.54.2
ns2.netangels.RU. 5 A 91.201.52.2
ns3.netangels.RU. 5 A 45.86.39.2
ns4.netangels.RU. 5 A 80.87.101.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0