Formula DAX such as COUNTIF in Excel

Hello! Help me please. 

I need formula DAX.

There is a table:

Campaign    Cost     ClientID

First            900        0001

First            900        0002

First            900        0003

Second       1000       0004

Second       1000       0005

Third           300        0006

I spent 2200 USD on three campaigns. 900 USD on "First", 1000 USD on "Second" and 300 USD on "Third".

And I got 6 Clients. I want to see how much I spent to get each Client.

What should I do to see 300 USD in "First"? Because it repeats 3 times.

The same thing with "Second". There should be 500 USD. Cause I got 2 clients from that Campaign and spent 1000 USD.

In Excel, it is easy to make))

=B2/COUNTIF(A:A;A2)

I'll be very appreciate for help!