There are math functions in the "Set a Small Integer Value", "Set an Integer Value", and "Set a Decimal Value" actions you can use (basic increment and decrement in the former, advanced features under the "Computed value" option in the latter two; You'd want to use the action appropriate to the datatype returned by "getValue").
Another option is the "{EXP:}" token, though that requires typing in the correct syntax, which the aforementioned actions do not.