Cut off two semicircles with diameters of 2 cm and 4 cm from a semicircle with a diameter of 6 cm. What is the perimeter of the figure in centimeters?
在一个直径为6厘米的半圆中再剪掉两个直径分别是2厘米和4厘米的半圆，现在图形的周长是多少厘米．
<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3.14 * 3</gadget>
<output>9.42</output>

<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">3.14 * 1</gadget>
<output>3.14</output>

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

<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

<gadget id="calculator">9.42 + 3.14 + 6.28</gadget>
<output>18.84</output>

<result>18.84</result>