I have two sheets open

On the first sheet, there is a single column of information.

On the second sheet, there is a single column of the same formula.

My question is what should the formula be if I want the second sheet's cells
to show the first sheet's information, but only if there is not the same
information in any of the cells above it? If there are any cells that
already hold the information, future cells should remain blank or "".

An Example...

Sheet 1 Column A Row 1 - "SS-DFC-4"
Sheet 1 Column A Row 2 - "S-DMC-5"
Sheet 1 Column A Row 3 - "SS-DFC-4"

Based on the above information sheet 2's Column A Row 1-3 should look like...

SS-DFC-4
S-DMC-5
""

Could i get some help on how to go about writing this formula?