There are 42 fifth-grade students participating in the "big health, big break" activity, including 30 people participating in the rope skipping team, 25 people participating in the shuttlecock kicking team, and each of them participated in at least one activity, and the fifth grade students participated in two activities How many people are participating?
五年级同学参加"大健康，大课间"活动有42人，其中参加跳绳队的有30人，参加踢毽子队的有25人，并且每人至少参加一项活动，五年级同学两项活动都参加的有多少人．
<gadget id="calculator">25 - 42</gadget>
<output>-17</output>

<gadget id="calculator">30 + (-17)</gadget>
<output>13</output>

<result>13</result>