The first shift picked 12 kilograms of tea leaves, the second shift picked 16 kilograms of tea leaves, and the third shift picked exactly twice the sum of the first two shifts. How many kilograms of tea leaves were picked by the third shift?
一班采茶叶12千克，二班采茶叶16千克，三班采的正好是前两班总和的2倍，三班采茶叶多少千克？
<gadget id="calculator">12 + 16</gadget>
<output>28</output>

<gadget id="calculator">28 * 2</gadget>
<output>56</output>

<result>56</result>