snail climbs up the pillar, climbs up 5 meters from early morning to evening every day, and slides down 4 meters at night. According to this climbing method, the snail climbed 20 days to reach the top of the pillar. How tall is this pillar?
一只蜗牛沿着柱子往上爬，每天清晨到傍晚向上爬5米，夜间又滑下4米，按这样的爬法，蜗牛爬了20天到达柱顶．这根柱子有多高？
<gadget id="calculator">5 - 4</gadget>
<output>1</output>

<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">1 * 19</gadget>
<output>19</output>

<gadget id="calculator">19 + 5</gadget>
<output>24</output>

<result>24</result>