In a certain school, 15 students are absent on Monday, 12 students are absent on Tuesday, and 9 students are absent on Wednesday. If there are 22 students who are absent for at least one day in these three days, how many students are there at most who are absent in these three days?
在某一学校，星期一有15个学生缺席，星期二有12个同学缺席，星期三有9个同学缺席．如果这三天至少有一天缺席的学生有22人，那么在这三天都缺席的学生最多有多少人．
<gadget id="calculator">9 - 22</gadget>
<output>-13</output>

<gadget id="calculator">15 + 12 + (-13)</gadget>
<output>14</output>

<gadget id="calculator">1 - 1</gadget>
<output>0</output>

<gadget id="calculator">1 + 1 + 0</gadget>
<output>2</output>

<gadget id="calculator">14 / 2</gadget>
<output>7</output>

<result>7</result>