input: Write a python function to add two numbers without using arithmetic operators.
  assert add_numbers(10, 5) == 15
  assert add_numbers(1, 2) == 3
  assert add_numbers(0, 0) == 0
  assert add_numbers(-1, 1) == 0
output: def add_numbers(a, b):
      while b != 0:
          carry = a & b
          a = a ^ b
          b = carry << 1
      return a