It is stipulated that 10 tons is recorded as 0 tons, 11 tons is recorded as +1 ton, and 9 tons are recorded as how many tons.
规定10吨记为0吨，11吨记为+1吨，则9吨记为多少吨．
<gadget id="calculator">10 - 9</gadget>
<output>1</output>

<result>1</result>