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

    def __str__(self):
        return str(self.data)



class LList:
    def __init__(self):
        self.head = None

    def is_empty(self):
        return self.head is None

    def prepend(self, data):
        self.head = Node(data, self.head)

    def pop(self):
        if self.head is None:
            raise ValueError("linklist is empty")
        e = self.head.data
        self.head = self.head.next
        return e

    def pop_last(self):
        if self.head is None:
            raise ValueError("linklist is empty")
        p = self.head
        if p.next is None:
            e = p.data
            self.head = None
            return e
        while p.next.next is not None:
            p = p.next
        e = p.next.data
        p.next = None
        return e

    # def find(self, pred):
    #     p = self.head

    def append(self, data):
        if self.head is None:
            self.head = Node(data)
            return
        p = self.head
        while p.next is not None:
            p = p.next
        p.next = Node(data)

    def printAll(self):
        p = self.head
        while p is not None:
            print(p.data, end='')
            if p.next is not None:
                print(', ', end='')
            p = p.next
        print('')



# l1 = LList()
# for i in range(3):
#     l1.prepend(i)
# for i in range(3, 5):
#     l1.append(i)
# l1.printAll()