Students from nine classes in the third grade went on a spring outing, and there were 68 people in each class. The number of people counted by the teacher has reached 599, how many people are still not here?
三年级九个班的同学去春游，每班都有68人．老师点人数，已到599人，还有几人没到？
<gadget id="calculator">68 * 9</gadget>
<output>612</output>

<gadget id="calculator">612 - 599</gadget>
<output>13</output>

<result>13</result>