There are 20 weeks in this semester, and there are 5 days of classes per week. Excluding the spring break and the "May 1st" holiday, there are 10 days in total. How many days are there actually classes in this semester?
这个学期有20周，每周上课5天，除去春假和"五一"长假一共10天，这个学期实际上课有多少天．
<gadget id="calculator">5 * 20</gadget>
<output>100</output>

<gadget id="calculator">100 - 10</gadget>
<output>90</output>

<result>90</result>