perform Macro based on cell value

Hello there, I have a worksheet with 20,000 rows.

I column A the value is either 0 or 1

For all the rows with a value of 1 - I would like a macro to paste the following formula into Column "R" of the corresponding row - for each row that has a value of 1 in column A.
Code:

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Please advise if this is possible?

Will give it a go cheers and let you know

Ho Mordred, I've inserted and ran the macro which took a few minutes to complete but I can;t see that its done anything - definitely not what it was intended to do anyway