The school held a hands-on ability competition, and there was a competition for tying ropes. On a 20-meter-long rope, tie a knot every 2 meters and leave no knots at both ends. How many knots should be tied in total?
学校举行动手能力大赛，其中有一项给绳子打结的比赛，在一条长20米的绳子上，每隔2米打一个结，两端不打结，一共应打多少个结．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>