A swimming pool with a length of 50 meters, Mr. Liu has swum 5 back and forth, how many meters has he swam?
一个长50米的游泳池，刘老师已经游了5个来回，他游了多少米．
<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">50 * 10</gadget>
<output>500</output>

<result>500</result>