Need Formula total in Crystal Report

Hi experts

i had created a crystal report and this  report is having 5 formula 

Now i need the sub total of all these 5 formula in another  new formula , For eg:-

A      +       B     +         C  +         D     +     E     =          ((F)   (A+B+C+D+E))

when i created the new formula field (F) adding all the 5 its working only when the all the 5 is having Values,, if any one Field is not having Value the

Total will not display

Pls help me to sort it

Regards