2 sheets in a workbook

Begin entering class participants on row 4

A=Last Name
B=First name
C= Address, etc.

Page 1 is patients
Page 2 is non-patients

Need a formula to calculate how many total partcipants there are since the
class has limited seating.

What formula can I insert in a cell on page one so I can see the the total
number of partcipants on both pages at a glance?

Thanks!