input: def convert_number(x: int) -> int:
      """ Convert a positive integer to negative or vice versa using bitwise NOT operator.
      >>> convert_number(5)
      -5
      >>> convert_number(-3)
      3
      """
      if x >= 0:
          return ~x + 1
      else:
          return ~(x - 1)
output:     if x >= 0:
          return ~x + 1
      else:
          return ~(x - 1)