Count number of all unique values down a column

Hi guys -

If I have a column with 300+ rows, some having an "X" value, others having a "NA" value.. how do I count how many x values appear in that column? I know you use a count formula, and use the whole column as the range, but I'm a little confused as to what to do afterwards.

I've attached a sample file for your reference. Look at column B. I know I can do a filter for the number of "X" values (whch is 39), but if there are a lot of columns this will get tedious. What formula can I use in the last cell to give me that final 39 count?

Thank you!!