Build a small payroll system.

1. Create an interface Payable with a method double pay().
2. Create an abstract class Staff that implements Payable. It has a protected String name field and a constructor. It does NOT implement pay() — subclasses must.
3. Create FullTimeStaff extending Staff. Constructor takes name and double monthlySalary. pay() returns monthlySalary.
4. Create ContractStaff extending Staff. Constructor takes name, double hourlyRate, and int hours. pay() returns hourlyRate * hours.

Do NOT write a main method.