The numerator of a fraction is the smallest composite number, and the denominator is 1 less than twice the numerator. If 14 is added to the denominator, how much should be added to the numerator to keep the size of the fraction unchanged.
一个分数的分子是最小的合数，分母比分子的2倍少1，如果把分母加上14，要使分数大小不变，分子应加上多少．
<gadget id="calculator">4 * 2</gadget>
<output>8</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">7 + 14</gadget>
<output>21</output>

<gadget id="calculator">21 / 7</gadget>
<output>3</output>

<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<result>8</result>