There are 30 students in a class, 20 of them signed up for the running event, 11 of them signed up for the jumping event, and 4 of them did not sign up for both. How many of them participated in both?
学校开运动会，某班有30名学生，其中20人报名参加赛跑项目，11人报名参加跳跃项目，两项都没有报名的有4人，问两项都参加的有几人？
<gadget id="calculator">4 - 30</gadget>
<output>-26</output>

<gadget id="calculator">20 + 11 + (-26)</gadget>
<output>5</output>

<result>5</result>