A total of 20 colorful flags were planted on one side of a road in the school. If a potted flower is placed between every two colored flags, how many potted flowers should be placed in total.
学校一条大路的一边共插了20面彩旗．如果每两面彩旗之间放一盆花，一共要放多少盆花．
<gadget id="calculator">20 - 1</gadget>
<output>19</output>

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

<result>19</result>