input: Write a function to find the median of a list of integers.
  assert find_median([3, 1, 2, 5, 4]) == 3
  assert find_median([7, 9, 4, 5]) == 6
  assert find_median([8, 12, 3, 6, 10, 5]) == 7
output: def find_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]