from typing import Union


def add(num1: Union[int, float], num2: Union[int, float]) -> Union[int, float]:
    return num1 + num2


print(add(1, 2))    # 3
print(add(3, 4.5))  # 7.5

list_a, list_b = [1, 2, 3], [4, 5, 6, 7]

joined_list = list_a + list_b
last_index = add(len(list_a), len(list_b)) - 1

reveal_type(last_index)             # Union[int, float]
assert isinstance(last_index, int)
reveal_type(last_index)             # Now it's int

print(joined_list[last_index])