Excel compare 2 columns/lists for differences or unique values

Hello,

In the attached spreadsheet, column A will be the prior month data always being dropped in as paste values. I will then drop the current month (new) data into column C. There will be more lines in column C every time for numbers that were added. I am looking for a formula so that I can do a conditional formatting to highlight and easily identify quickly what numbers are new and not in column A. Can someone please help?


Thanks!