class Queue:

def __init__(self):

self.array = []

def enqueue(self, elem):

self.array.append(elem)

def dequeue(self):

if not self.array:

return None

else:

return self.array.pop(0)

def __str__(self):

return ", ".join(self.array)

def __add__(self, other):

new_q = Queue()

new_q.array = self.array[:]

new_q.enqueue(other)

return new_q

def __iadd__(self, other):

self.enqueue(other)

return self

def __neg__(self):

return self.dequeue()

def __len__(self):

return len(self.array)