A miser always likes to divide a loaf of bread into many sections to eat. It takes 20 seconds to divide a loaf of bread into 5 sections, so how many seconds will it take to divide a loaf of bread into 4 sections?
吝啬鬼总喜欢把一条面包分成很多段吃，把一条面包分成5段用20秒，那么分成4段要用多少秒．
<gadget id="calculator">5 - 1</gadget>
<output>4</output>

<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>