# Here is our Stack Class

class Stack:

def __init__(self):

self.items = []

def size(self):

return len(self.items)

def push(self, item):

self.items.append(item)

def pop(self):

if self.size()==0:

return None

else:

return self.items.pop()

class Queue:

def __init__(self):

# Code here

self.ins = Stack()

self.out = Stack()

def size(self):

# Code here

return self.ins.size()+self.out.size()

def enqueue(self,item):

# Code here

self.ins.push(item)

def dequeue(self):

# Code here

if self.out.size() == 0:

while self.ins.items:

self.out.push(self.ins.pop())

return self.out.pop()

queue = Queue()

queue.enqueue(5)

print(queue.ins.items, queue.out.items)

queue.enqueue(10)

queue.enqueue(20)

queue.enqueue(15)

print(queue.dequeue())

print(queue.ins.items, queue.out.items)

print(queue.dequeue())

print(queue.ins.items, queue.out.items)

print(queue.dequeue())

print(queue.ins.items, queue.out.items)

print(queue.dequeue())

print(queue.ins.items, queue.out.items)

print(queue.dequeue())

print(queue.ins.items, queue.out.items)