input: Write a function to find the median of a list of numbers.
  assert median([1, 3, 3, 6, 7, 8, 9]) == 6
  assert median([1, 2, 3, 4, 5, 6, 8, 9]) == 4.5
  assert median([10, 20, 30]) == 20
  assert median([5, 3, 1, 2, 4]) == 3
output: def median(numbers):
      numbers.sort()
      n = len(numbers)
      mid = n // 2
      
      if n % 2 == 0:
          return (numbers[mid - 1] + numbers[mid]) / 2
      else:
          return numbers[mid]