How to iterate an if statement

[ahart56]

I am creating a worksheet that looks up member sizes from a user input. I have made it so that when the user types in the beam size it returns "doesn't exist" or the dimensions of the beam in number form. Now i want the numbers to appear in a cell but i cant figure out how to write the formula the way i want it. Basically I need the cell to return:

=if(a6="doesn't exist", if(a7="doesn't exist", if(a8="doesn't exist" .... this continues until next cell is empty or if it encounters a number in which case i want it to return that number.

I'm pretty sure this is easy if you know macros or programming but I dont so please help!

Thank you,
AH