Count one column when a 2nd column matches values in a 3rd column.

I have an issue which I think countif works for but I cannot figure it out:

One one spreadsheet I have two columns:
Site # Active or Placebo
15 a
15 p
18
16
24 p
17 a
18 a
16 p
17 a
18 p
25 a
13
12 p
22 a
22 a
15 a
19 a
16 p
13 a
20 a
15 p

On a second spreadsheet I have a column matching "Site#" above (same site numbers).

I want to count the number of non blank cells in the "Active or Placebo" column on the first spreadsheet that have site numbers in the "Site #" column that correspond with the same site number on the 2nd sheet -

So my second sheet would look like:

Site # # Subjects
15 4
16 0
17 2
etc.

I have tried countif and it does not seem to have enough variables. Sumif doesnt seem to work either or I am not applying it correctly. Any help would be appreciated.

Thanks for your help that worked great!!!