todo = []
answer = ""

while answer != "exit":
    answer = input("Please specify a command [list, add, mark, archive, exit]: ")

    if answer == "list":
        print("You saved the following to-do items:")
        for index, item in enumerate(todo):
          print(index + 1, "[x] " if item[0] else "[] ", item[1])

    elif answer == "add":
        item = input("Add an item: ")
        while len(item) == 0:
            item = input("Add an item: ")
        else:
            todo.append([False, item])
            print ("Item added")

    elif answer == "mark":

        print("You saved the following to-do items:")
        for index, item in enumerate(todo):
          print(index + 1, "[x] " if item[0] else "[] ", item[1])

        index = int(input("Which one you want to mark as completed:"))
        todo[index - 1][0]= True


        print("You have marked the following to-do items:")
        for index, item in enumerate(todo):
            print(index + 1, "[x] " if item[0] else "[] ", item[1])

    elif answer == "archive":
        for i in todo:
            if i[0] == True:
            todo.remove[i]
            print("All completed tasks got deleted.")
            else
            print("You have no completed tasks.")