Change cell reference mutliple sheets formula

Hello,

I have 7 spreadsheets that I am currently using the IF formula for. These spreadsheets all have the same format so currently the formulas sits at:

=IF(Sheet1!C5="",Sheet2!C5,Sheet1!C5)

This is want I am trying to say, if Column C has one of the cells that is empty, then move to column C in the next sheet and so forth. The problem is sheet 2 does not start specificly with cell 'C5', instead, it references with the cell in the previous sheet.

Example:
=IF(Sheet1!C6="",Sheet2!C6,Sheet1!C6), all at C6's
=IF(Sheet1!C7="",Sheet2!C7,Sheet1!C7), all at C7's
=IF(Sheet1!C8="",Sheet2!C8,Sheet1!C8), all at C8's

I want each sheet to start at cell C5 no matter where the previous sheet cell ends off. When it finds a cell in column C that is empty, go to the next sheet starting at C5.

I hope I made sense.

Thanks in advance for helping.

Olivia