input: Write a function to convert a positive integer to negative or vice versa using bitwise NOT operator.
  
  def convert_to_negative(x):
      return ~x + 1
  
  def convert_to_positive(x):
      return ~(x-1)
  
  assert convert_to_negative(10) == -10
  assert convert_to_negative(-5) == 5
  assert convert_to_positive(15) == -15
  assert convert_to_positive(-8) == 8
output: def convert_to_negative(x):
      return ~x + 1
  
  def convert_to_positive(x):
      return ~(x-1)