how to change text in every other row of a column

Hey guys real simple problem here.
All I am trying to accomplish is

the pattern you see every other row in column C I need to have a "-R" on the end of the number.

on odd rows I need each cell in Column C to have "-R" at the end of text



try to get help excel.png

Please help

thank you,

Please try at C2

=A2&IF(MOD(ROW(A2),2),"-R","")

or
=A2&IF(A1=A2,"-R","")

Are you trying to delete duplicates?