piece of paper, tear it into 4 pieces for the first time, and tear one of them into 4 pieces for the second time, and so on, how many small pieces of paper will be obtained after the 4th time of tearing.
一张纸片，第一次把它撕成4片，第二次把其中一片又撕成4片，…如此下去，第4次撕后共得小纸片多少片．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">1 + 12</gadget>
<output>13</output>

<result>13</result>