Xiao Ming's family lives on the 6th floor. He and his father started to play the game of "scissors, rock and paper" from the 4th floor to go upstairs. On the 20th time, Dad and Xiaoming both went up from the 4th floor to the 6th floor, so how many steps are there between the two floors?
小明家住在6楼，他和爸爸从4楼开始玩"剪刀、石头、布"的游戏上楼，规定每次获胜者可以上3级台阶，输的人就得下1级台阶，当玩到第20次时，爸爸和小明都从4楼上到了6楼，那么这两层之间有多少个台阶．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<result>20</result>