class queue():
    
    # Constructs an empty queue
    def __init__(self):
        self.L = []
        self.start = -1 # initialize start to point to before the first valid index

    # Enqueue appends items at back of list
    def enqueue(self, item):
        self.L.append(item)
        # If the queue was empty prior to this insertion, update start
        if self.start == -1:
            self.start = self.start + 1

    # Dequeue removes items from front of list. This method is not efficient 
    def dequeue(self):
        self.start = self.start + 1
        item = self.L[self.start - 1]
        return item
    
    # Shows the queue as a list
    def __repr__(self):
        return str(self.L[self.start:])
    
    # Queue is empty is there if the list if physically empty
    # or start points to the end of the list
    def isEmpty(self):
        return len(self.L) == 0 or self.start == len(self.L)