pcDNA 3.1/pTarget and stable cell line - (Nov/24/2005 )

I have a question here. Please kindly answer.
I have transduced a cell line with two different retroviral vectors to make a double stable cell line. The two vectors carry different markers, neo and puro respectively. Now I am going to start the antibiotics treatment. Can I add both antibiotics together at the same time or should i select with one antibiotics first followed by the other?