public int numOfBook() {
		ArrayList<Card> list = getList();
		HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
		Integer bookNum = null;
		for (int i = 0; i < list.size(); i++) {
			int numb = list.get(i).getCardNum();
			if (!map.containsKey(numb)) {
				map.put(numb, 1);
			} else {
				int qty = map.get(numb) + 1;
				map.put(numb, qty);
			}
		}
		for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
			Integer key = entry.getKey();
			Integer value = entry.getValue();
			if (value == 4) {
				bookNum = key;
				break;
			}

		}
		return bookNum;
	}