Apex domains cannot have CNAME records.
Question and response
Question
dig DELTATELESYSTEMS.RU. NS
Answer
DELTATELESYSTEMS.RU. 5 NS ns2.DELTATELESYSTEMS.RU.
DELTATELESYSTEMS.RU. 5 NS ns1.DELTATELESYSTEMS.RU.
Authority
The response has no authority records.
Additional
ns1.DELTATELESYSTEMS.RU. 5 A 91.206.16.2
ns2.DELTATELESYSTEMS.RU. 5 A 91.206.17.253
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0