How to count the amount of pins that a particular circuit uses

Question

For a circuit like this:

How do you decide how many pins would be needed? Listening back to the lecture someone declared it as 19, but I don't know where that value has came from. Could someone explain or the label the diagram for how we get 19 ?

Answer 1

19 pins = 9 inputs + 8 outputs + 1 power + 1 ground