Given that a is a prime number and 2013-a is an odd number, what is the area of a circle with a radius of a.
已知a是一个质数，且2013-a是奇数，那么半径为a的圆面积是多少．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>12.56</result>