Что выведет код?

from collections.abc import Iterable
def f(arr):
    s = 0
    items = list(arr)
    while items:
        first = items.pop(0)
        if not isinstance(first, Iterable):
            s += first
        else:
            items.extend(first)
    return s
print(f((1, (2, (3, (4, (5)))))))