Captivate 9 Advanced Action - Expression

Hello, all.  

Any chance someone knows whether or not I can have multiple operations in the same expression?

For example, I would like to have this as one expression:

Expression         vTOTAL = v1 + v2 + v3 + v4

However, all I can do is:

Expression        vTOTAL = v1 + v2

That said, I have tried:

Expression       vTOTAL = vTOTAL + v1

Expression       vTOTAL = vTOTAL + v2

Expression       vTOTAL = vTOTAL + v3

Expression       vTOTAL = vTOTAL + v4

With the last example, the numerical progression of my vTOTAL variable is: 0, 1, 3, 6, 12 (and v1 through v4 are all assigned the value of 1)

What am I missing?  I've included my advanced actions below. Thank you!