Summing rows where adjacent cell is the same

I have a question which on the face of it seems very simple but have not found a solution whilst searching this and many other forums.
I am using Excel 2010 and have a list of customer numbers with associated revenue. In this list the same customer number will appear repeatedly for each sale. In reality the list is over 2000 lines long with a possibility of 300 different customers.

What I want is an output than sums the total per customer number, but cannot reference the customer number in any formulae as I will not know it in advance.
The output should look like this


I have tried with a formulae that says something like =SUMIF(A1:A2000,"criteria",B1:B2000) where criteria = 11111, however what I want is a similar formulae that dynamically subtotals all the sales per customer without me having to know in advance the customer number. I want the formulae to learn the criteria from the given data.

Any help is appreciated.

You'll need two formulas for this. Note that the Customer IDs must be text (use an apostrophe if needed).

Wow that was quick and yes these two formulaes look like they will work.
The customer numbers are indeed text as extracted.
Thanks again CheshireCat.