Generate a numerical sku based on product number

I need to create a 4 digit sku for my items. The sku should increase for every product number that is different. If the product number is the same then the sku stay the same for that item.

The sku should start at 1100 and work its way up from there.

I have attached an example. I have around 10,000 sks so automating this would be helpful.

I remembering doing something similar to this but can not remember how I did it.

Thanks for your help in advance.

sku example.xlsx

Works perfect. Thanks.