The 44 students brought 9 yuan, 10 yuan, 11 yuan, ..., 52 yuan respectively, and each of them used up all the money to buy a notebook for themselves. There are only two kinds of notebooks, one for 3 yuan and one for 5 yuan. So, how many notebooks of 3 yuan did they buy at least?
44名同学分别带了9元、10元、11元、…、52元钱，每人都把钱全部用完，给自己买笔记本．笔记本只有两种，3元一本和5元一本．那么，他们最少共买多少本3元的笔记本．
<gadget id="calculator">2 * 9</gadget>
<output>18</output>

<gadget id="calculator">4 * 9</gadget>
<output>36</output>

<gadget id="calculator">1 * 9</gadget>
<output>9</output>

<gadget id="calculator">18 + 36 + 9 + 18</gadget>
<output>81</output>

<result>81</result>