In the first sports meeting in the Hubin New District, there were three running events: 100 meters, 400 meters and 1000 meters. Some of the fifth grade students participated in one of them, some participated in two of them, and some participated in all three events. How many kinds of registrations are there for running competitions among the fifth graders?
湖滨新区首届运动会中有100米、400米、1000米三项跑步比赛，五年级同学中有的参加其中一项，也有的参加了其中两项，还有的三项都参加了．五年级同学中跑步比赛报名情况一共有多少种？
<gadget id="calculator">3 + 3 + 1</gadget>
<output>7</output>

<result>7</result>