Formula to search a Column with Cell content from another Column?

I'm trying to compare two columns of user names against each other so I can delete obsolete users in the 2nd column.

IE Column A has:
JaneDoe
JohnDoe
JaneSmith

Column C has:
JaneDoe
JohnDoe
JohnSmith
JaneSmith


I've tried =IF(A:A=C1, "Keep", "Delete") and that doesn't work because it's looking for "=C1" in the A column. I have also tried =IF(ISNUMBER(SEARCH("JaneDoe",A:A)),"OK", "Not OK") which does work in searching the entire column A but I have over 900 rows in both columns and don't want to edit each individual search where JaneDoe is put and want it to do a cell reference from C instead.

Any suggestions?