A worm is crawling on the grid line. Its initial position is A(2, 2), it first climbs to B (2, 4), then to C (5, 4), and finally to D, (5 , 6), then how many units the worm has crawled.
一只小虫在方格的线路上爬行，它初始位置是A(2，2)，先爬到B(2，4)，再爬到C(5，4)，最后爬到D、(5，6)，则小虫共爬了多少个单位．
<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">2 + 3 + 2</gadget>
<output>7</output>

<result>7</result>