SQL: display note for specific string combine with column

Hello Guru,

Having below sample data

create table XXTEST (DOCNBR VARCHAR(10),RNBR VARCHAR(20));

insert into XXTEST (DOCNBR,RNBR) values ('149610978','149610978-B1');

insert into XXTEST (DOCNBR,RNBR) values ('149610978','149610978-B2');

insert into XXTEST (DOCNBR,RNBR) values ('149610978','149610978-C1');

insert into XXTEST (DOCNBR,RNBR) values ('149610978','149610978-C2');

insert into XXTEST (DOCNBR,RNBR) values ('149610978','149610978-S1');

What I want is to display 'SPECIAL' if in RNBR I have combination of DOCNBR and -S. I tried below query but no luck. Please advise

SELECT X.DOCNBR,X.RNBR,

CASE  WHEN X.DOCNBR ||'-S' = X.RNBR