Build a cylindrical cistern with a depth of 3 meters and a diameter of 4 meters at the bottom. How many square meters does this cistern occupy?
修一个深3米，底面直径4米的圆柱形蓄水池，这个蓄水池占地多少平方米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>