How do I add two column values in a table with CQL?

I am needing to add two values together to create a third value with CQL. Is there any way to do this? My table has the columns number_of_x and number_of_y and I am trying to create total. I did an update on the table with a set command as follows:

UPDATE my_table
SET total = number_of_x + number_of_y ;

When I run that I get the message back saying:

no viable alternative at input ';'.