Combining COUNTIF and OR [SOLVED]

hi everyone,

In a range, by example C2:C20, I have everytime one letter of the alphabet (for the moment only A, B, C, D or E)

I would like to count the number of As and Bs

For the moment I have solved my problem by adding both counts:
=COUNTIF(C2:C20,"A")+COUNTIF(C2:C20,"B")

But since I intend to extend the range and the number of letters to count, I'd like to know if there is a way to write, by example

=COUNTIF(C2:C20,"A" OR "B")