def find_min(element):
    """TODO: complete for Step 1"""
    if element == []:
        return -1

    for i in element:
        if type(i) != type(1):
            return -1
    #         break

    if len(element) != 1:
        if element[0] < element[1]:
            element.pop(1)
        elif element[0] > element[1]:
            element.pop(0)
        elif element[0] == element[1]:
            element.pop(0)
        return find_min(element)
    print(element[0])
    return int(element[0])





def sum_all(element):
    """TODO: complete for Step 2"""

    if element == []:
        return -1


    for i in element:
        if type(i) != type(1):
            return -1

    if len(element) == 1:
        return element[0]

    else:
        # print(element[0] + sum_all([element[1:]])
        return (element[0] + sum_all(element[1:]))


def find_possible_strings(character_set, n):
    """TODO: complete for Step 3"""

    list_ = []
    prefix = ""
    if len(character_set) == 0:
        return []

    for i in character_set:
        if type(i) != type("a"):
            return list_


    for i in character_set:
        if n == 1:
            return character_set

        for i in character_set:
            for j in find_possible_strings(character_set, n-1):
                list_.append(i + j)
        return(list_)

print(find_possible_strings(['a','b'],3))