class Node:
    def __init__(self, data):
        self.data = data
        self.next = None

class my_linked_list:
    def __init__(self):
        self.head = None
        self.last_node = None

    def add_value(self, my_data):
        if self.last_node is None:
            self.head = Node(my_data)
            self.last_node = self.head
        else:
            self.last_node.next = Node(my_data)
            self.last_node = self.last_node.next

    def print_it(self):
        curr = self.head
        while curr:
            print(curr.data)
            curr = curr.next

    def alternate_nodes(self):
        curr = self.head
        while curr:
            print(curr.data)
            if curr.next is not None:
                curr = curr.next.next
            else:
                break

my_instance = my_linked_list()
my_list = input("输入链表元素：").split()
for elem in my_list:
    my_instance.add_value(elem)
print("链表中的交替元素为：")
my_instance.alternate_nodes()

输入链表元素：56 78 43 51 23 89 0 6
链表中的交替元素为：
56
43
23
0