The first class picks 12 kilograms of tea leaves, which is 4 kg less than the second shift, and the third shift picks exactly twice the sum of the first two shifts. How many kilograms of tea leaves are picked by the third shift?
一班采茶叶12千克，比二班少采4千克，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 + 12 + 4</gadget>
<output>28</output>

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

<result>56</result>