There are a number of primary school students forming a circle, start counting from a certain student according to 1, 2, 3... If clockwise, then when reporting to Xiaomei, she should report "15"; if counterclockwise, Xiaomei The United States should report "7". So, how many pupils are there in this group?
有若干名小学生围成一个圆圈，从某一个学生按1、2、3…开始报数，若按顺时针方向，那么报到小美时，她应该报"15"；若按逆时针方向，小美应报"7"．那么，这群小学生一共有多少名．
<gadget id="calculator">7 - 2</gadget>
<output>5</output>

<gadget id="calculator">15 + 5</gadget>
<output>20</output>

<result>20</result>