A certain school held a New Year's fitness activity, and Class One of the sixth grade participated in two competitions. 30 people participated in the long-distance running, and 28 people participated in the rope skipping. Among them, 13 people participated in these two activities at the same time. How many people in Class 61 participated in the New Year's fitness activities?
某校举行迎新年健身活动，六年级一班参加了两项比赛．有30人参加了长跑，28人参加了跳绳．其中同时参加这两项活动的有13人．六一班有多少人参加了迎新年健身活动．
<gadget id="calculator">28 - 13</gadget>
<output>15</output>

<gadget id="calculator">30 + 15</gadget>
<output>45</output>

<result>45</result>