Match two excel column and output the matched value in C an D column

Hi,
I have multiple excel files like this structure,I’d like to have the output highlighted in green,the logic is if B is in Column A then Output the value in column B; If B is not in Column A, then Output B.
I really not know how to achieve them,I’d appreciate if you could give me some sight.
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Import Column A and Column B into datatables and compare them. You can either do that in the UiPath GUI, https://youtu.be/e4_qR4jT2xI, or with C# LINQ, https://youtu.be/4OsTxNTHMlM