Filling Series for Referenced Workbooks

[ericlb7]

Hey people,

I need help filling a series based on a referenced workbook.

Here is my formula:

=[CIF9000.xls]Sheet1!$A$1

I want to be able to fill down a series that only increments my referenced workbook.

So, filling the series would look like this:
=[CIF9000.xls]Sheet1!$A$1
=[CIF9001.xls]Sheet1!$A$1
=[CIF9002.xls]Sheet1!$A$1

Thanks in advance!

-Eric