def remove_duplicates(self):
    if self.head is None:
        return
    target = curr = self.head
    while curr is not None:
        if curr.next is not None:
            if curr.next.value == target.value:
                curr.next = curr.next.next
                self.length -= 1
        else:
            target = curr = target.next
        curr = curr.next

# Output:
# Before: [2, 3, 1, 2, 4, 5, 4, 4, 2, 3, 2, 5, 4]
# After: [2, 3, 1, 4, 5, 4, 5]