There are 45 people in class one of the third grade participating in the rope skipping and volleyball competition, 22 people participating in the rope skipping competition, and 28 people participating in the volleyball competition. How many people participated in both competitions?
三年级一班有45人参加跳绳和排球比赛，参加跳绳比赛的有22人，参加排球比赛的有28人，两项比赛都参加的有多少人．
<gadget id="calculator">28 - 45</gadget>
<output>-17</output>

<gadget id="calculator">22 + (-17)</gadget>
<output>5</output>

<result>5</result>