def XOR(bits1, bits2):
	"""perform a XOR operation and return the output"""
  # Assuming both bit string of same length
	xor_result = ""
	for index in range(len(bits1)):
		if bits1[index] == bits2[index]: 
			xor_result += '0'
		else:
			xor_result += '1'
	return xor_result