study online. There is a counting method that is binary, that is, when the number is full two, the previous one is carried forward by one. Huanhuan has a binary number 1101 in his hand. How much should this number be represented in decimal?
网上学习．有一种计数法是二进制的，即满二向前一位进一．欢欢手中有一个二进制数为1101，这数用十进制表示应该是多少呢？
<gadget id="calculator">2 ** 3</gadget>
<output>8</output>

<gadget id="calculator">1 * 8</gadget>
<output>8</output>

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

<gadget id="calculator">1 * 4</gadget>
<output>4</output>

<gadget id="calculator">2 ** 1</gadget>
<output>2</output>

<gadget id="calculator">0 * 2</gadget>
<output>0</output>

<gadget id="calculator">2 ** 0</gadget>
<output>1</output>

<gadget id="calculator">1 * 1</gadget>
<output>1</output>

<gadget id="calculator">8 + 4 + 0 + 1</gadget>
<output>13</output>

<result>13</result>