class Node :

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


class doublelinkedlist :

    def __init__(self):
        self.head = None

    def prepend(self,new_data):
        new_node = Node(new_data)
        new_node.next =self.head
        if self.head is not None :
            self.head.prev = new_node
        self.head = new_node

    def append(self,new_data):
        new_node = Node(new_data)
        new_node.next = None

        if self.head is None :
            new_node.prev =None
            self.head = new_node
            return

        last = self.head
        while last.next is not None:
            last = last.next
        last.next = new_node
        new_node.prev =last
        return

    def insert_after(self,key,new_data):
        curr = self.head
        while curr :
            if curr.next is None and curr.data == key:
                self.append(new_data)
            elif curr.data == key:
                new_node = Node(new_data)
                nxt = curr.next
                curr.next = new_node
                new_node.next = nxt
                nxt.prev = new_node
            curr = curr.next

    def insert_before(self, key, data):
        curr = self.head
        while curr:
            if curr.prev is None and curr.data == key:
                self.prepend(data)
            elif curr.data == key:
                new_node = Node(data)
                prev = curr.prev
                prev.next = new_node
                curr.prev = new_node
                new_node.next = curr
            curr = curr.next

    def printlist(self):
        temp = self.head
        while temp is not None :
            print temp.data,
            temp = temp.next

list1 = doublelinkedlist()
list1.prepend(2)
list1.append(3)
list1.append(5)
list1.append(7)
list1.prepend(1)
list1.insert_before(5,4)
list1.insert_after(5,6)
list1.printlist()