An Array formula.

=SUM(IF(FREQUENCY(IF(B2:B16=F3,IF(LEN(A2:A16)>0,MATCH(A2:A16,A2:A16,0),"")),IF(B2:B16=F3,IF(LEN(A2:A16)>0,MATCH(A2:A16,A2:A16,0),"")))>0,1))