When a=0.5, b=1, c=2, what is the value of 2c-ab
当a=0.5，b=1，c=2时，2c-ab的值是多少
<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<gadget id="calculator">0.5 * 1</gadget>
<output>0.5</output>

<gadget id="calculator">4 - 0.5</gadget>
<output>3.5</output>

<result>3.5</result>