Counting unique instances above a certain quantity

Hello. If you have a list of customers (for example, A, A, B, B, B, C, C, C, C) how can you can count the numbers of customers with over a certain amount of entries. So, for example if a customer is in 4 rows, I want that to be counted as 1, but not if a customer just has three rows. It's sort of a mix of unique count plus a conditional.

Thanks for responding but I don't think I explained myself clearly. Let's say you have a list of customers and some of those customers appear multiple times in a list. You can use a formula in excel to get a unique count of customers, so just counting the customers and not the amount of times they appear in the list. I want to do something similar BUT I want to count the unique customers that appear more than 3 (or x) times in the list. Make sense?

The customers would all be in the same column, unless you are proposing something different. Here is a simple spreadsheet with the result that I want (obviously, the spreadsheet I'm looking at has thousands of rows).

@shg. What are you doing with column D. I don't understand.

And how would you do that with formulas? I have 50,000 rows haha. I ended up using pivot tables but I'd still be interested in learning how to do it with formulas. Thanks.