HOW-TO Limit the number of files created

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I am writing a macro that will automatically create a file BUT I want to limit the number of files that the folder will hold to three.
So the macro will firstly determine how many files are in the folder and create a new one IF there are only two files.
Could someone provide me with a simple example of this? (or point me to the documentation for this)
AND AS ALWAYS, this is GREATLY appreciated!
Kent