Yangyang and Liangliang want to buy the same book. Yangyang brought 18 yuan, and Liangliang brought 22 yuan. The sum of their money is just enough to buy 2 books. They bought 2 books, how much should Yangyang give Liangliang when they go back?
洋洋和亮亮想买同一本书．洋洋带了18元，亮亮带了22元．他俩的钱加起来刚好能买2本书．他们买了2本书，回去后，洋洋应该给亮亮多少元？
<gadget id="calculator">18 + 22</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 - 18</gadget>
<output>2</output>

<result>2</result>