enQStack = new Stack()
deQStack = new Stack()

enqueue(num):
	# push all new elements to enqueue stack O(1)
	enQStack.push(num)

dequeue():
	# if dequeue stack has elements pop from it O(1)
	# else fill dequeue stack with elements from enqueue stack O(n), then pop from it
	if deQStack is empty:
		fillDeQStack()
	deQStack.pop()

peek():
	# if dequeue stack has elements peek from it O(1)
	# else fill dequeue stack with elements from enqueue stack O(n), then peek from it
	if deQStack is empty:
		fillDeQStack()
	deQStack.peek()

fillDeQStack():
	# fill dequeue stack with elements from enqueue stack O(n), dequeue = reversed enqueue
	while enQStack is not empty:
		deQStack.push(enQStack.pop())