from typing import List


def find_unused_bank(edge_banks: List[int]) -> int:
    """
    Given a list of banks used in one clock, find a bank index that isn't used, or -1 if all are used
    :param edge_banks:
    :return:
    """
    for i in list(range(len(edge_banks))):
        if i not in edge_banks:
            return i
    return -1