Find empty cell between cells with value

Hi Forum,

I hope you can help me out here :-). I'm looking for a formula that can help me identifying a blank cell (without value) between a range of cells with 1 as value.

When a blank cell in a row is identified, I would like a marker (e.g. letter X) as return value.

Example 1 where I would like to identify that there is a blank/an empty cell between C77 and E77:

Row no.        Col. A      Col. B      Col. C      Col. D      Col. E
77                [blank]      [blank]          1          [blank]          1


Example 2 where I would like to identify that there are blanks/empty cells between A253 and C253 and between C253 and E253:

Row            Col. A      Col. B      Col. C      Col. D      Col. E
253                  1          [blank]          1            [blank]          1

Sorry, that I can't show the examples with spacing.

How can I write a formula that identify these blank cells?

Thanks in advance for your help.

Kind regards,
Arne