input: Write a python function to classify salaries into low, medium, and high categories.
  assert classify(10000) == "low"
  assert classify(15000) == "medium"
  assert classify(30000) == "medium"
  assert classify(35000) == "high"
output: def classify(salary):
      if salary < 15000:
          return "low"
      elif salary <= 30000:
          return "medium"
      else:
          return "high"