public class MyQueueImpl implements MyQueue {
	private Node head;
	private Node tail;
	private int size;
	
	public MyQueueImpl() {
		head = null;
		tail = head;
		size = 0;
	}
	
	public int pop(){
		if (isEmpty()) {
			throw new RuntimeException("---");
		}
		int result = head.value;
		head = head.next;
		size--;
		return result;
	}
	
	public void push(int num) {
		if (isEmpty()){
			head = new Node(num);
			tail = head;
		} else{
			tail.next = new Node(num);
			tail = tail.next;
		}
		size++;
	}

	public boolean isEmpty() {
		return size == 0;
	}
}