Workbook.SaveAs function, appends number to similar named files

[Cheesecube]

Hi, how do you modify the Workbook.SaveAs function to append a number based on whether there are similarly named files in the same folder?

E.g. Set the filename as Output_n.xlsx

If it is the first file that has the name, then save the file as Output_1.xlsx

If it's the second or third file that has the name, save the file as Output_2.xlsx or Output_3.xlsx

If it's the 12th file that has the name, save the file as Output_12.xlsx

and so on