Workflow 'add' function

I am using the workflow ‘add’ function to sum a number (16) of parameters together.

This seems to work fine with 2 parameters, but not more than that.

Is there a parameter limit on this function, and if so, how do I sum all 16 fields. Do I need to embed a number of ‘add’ functions in a single statement?

I am not sure, but I think the way to achieve it is with nesting, something logically similar to

add(1, add(2, add(3, 4)))

but I don’t have the exact syntax here.