In an exam, there are 30 people who are excellent in mathematics, 28 people who are excellent in Chinese, 18 people who are excellent in both subjects, and how many people are excellent in at least one of the two subjects?
在一次考试中，数学得优秀的有30人，语文得优秀的有28人，两门都得优秀的有18人，两门功课中至少一门得优秀的有多少人？
<gadget id="calculator">28 - 18</gadget>
<output>10</output>

<gadget id="calculator">30 + 10</gadget>
<output>40</output>

<result>40</result>