There is a semicircular board, its diameter is 4 decimeters, what is its circumference in decimeters?
有一块半圆形的木板，量得它的直径是4分米，它的周长是多少分米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">6.28 + 4</gadget>
<output>10.28</output>

<result>10.28</result>