The fifth grade participates in the summer camp activities. There are 7 people in a group and 6 people, 8 people in a group with 7 people, and 9 people in a group with 8 people. How many people should participate in the summer camp at least?
五年级参加夏令营活动7人编成一组多6人，8人编成一组多7人，9人一组多8人，参加夏令营至少有多少人？
<gadget id="calculator">7 * 8 * 9</gadget>
<output>504</output>

<gadget id="calculator">504 - 1</gadget>
<output>503</output>

<result>503</result>