input: Write a python function to calculate the average salary of employees in a company.
  assert calculate_average_salary(company) == 27500
  employee3 = Employee('Jim Beam', 35, 40000)
  company.add_employee(employee3)
  assert calculate_average_salary(company) == 31666.67
output: def calculate_average_salary(company):
      total_salary = sum(employee.salary for employee in company.employees)
      average_salary = total_salary / len(company.employees)
      return round(average_salary, 2)
  
  class Employee:
      def __init__(self, name, age, salary):
          self.name = name
          self.age = age
          self.salary = salary
  
  class Company:
      def __init__(self):
          self.employees = []
  
      def add_employee(self, employee):
          self.employees.append(employee)
  
  # Example usage:
  employee1 = Employee('John Doe', 30, 30000)
  employee2 = Employee('Jane Smith', 25, 25000)
  company = Company()
  company.add_employee(employee1)
  company.add_employee(employee2)