def main():

    skip_list = SkipList()
    skip_list.insert(2, "2")
    skip_list.insert(4, "4")
    skip_list.insert(6, "4")
    skip_list.insert(4, "5")
    skip_list.insert(8, "4")
    skip_list.insert(9, "4")

    skip_list.delete(4)

    print(skip_list)