If a cell is not blank subtract the next cell in the same column that is not blank

Hello,
I have a column (Column A) with a formula that only returns values on certain rows otherwise it returns "". I need a formula for column B that subtacts the next value in the column skipping over the blank ("") ones.
For example
Column A : 5 ,"","","","",3,"","","",-2,"","","","","","",9
Column B : 2 ,"","","","",5,"","","",-11,"","","","","","",""
column B is what I would like to achieve where the B1 would be A1-A6, B6 would be A6-A10, and B10 would be A10-A17
Thanks in advance.