Ignoring blank fields in simple formula

Ignoring blank fields in simple formula

Hi All

I'm trying to create a formula expression to sum four fields using this expression:

"£ " + ((Presentation_Cost  +  Press_Release_Cost  +  Other_Costs  +  Deliveries).round(2))

which works fine, unless one of the four fields are blank and then the result is also blank. What do I need to change it to so that the formula will ignore blank fields?

Many thanks

Nick