What should be the logic of selecting a number for uniqueness?

Question

Python

Help me figure it out. There is a first integer, and there are two lists of integers, you need to compare the first number with these two lists. Suddenly, if the first number is in one of these lists, then you need to add one to it and again go through these two lists. And so on until the first number is in any lists, then stop the whole process. I can not figure out how to do this, tell me, preferably with a ready-made code)))

Answer 1

That is, while the number is in list1 or if the number is in list2, add one, otherwise stop?

while number in list1 or number in list2:
    number += 1
print('stop', number)

complex algorithmization, however