The street where a postman delivers letters is shown in Figure 3, and the numbers on the figure represent the kilometers of each section of the street. He started from the post office, walked through the streets, and finally returned to the post office. Q: What is the most reasonable route to take? How many kilometers will the whole journey take?
一个邮递员投送信件的街道如图3所示，图上数字表示各段街道的千米数．他从邮局出发，要走遍各街道，最后回到邮局．问：走什么样的路线最合理？全程要走多少千米？
<gadget id="calculator">1 + 2 + 4 + 2 + 1</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">2 * 4</gadget>
<output>8</output>

<gadget id="calculator">20 + 18 + 8</gadget>
<output>46</output>

<result>46</result>