The bus runs every 5 minutes from A to B, and the whole journey takes 15 minutes. When a person goes from B to A, he meets a bus at the beginning and 10 buses on the way. How many minutes did the person walk before leaving?
公交车从甲到乙每5分钟一趟，全程要开15分钟，一个人从乙到甲，开始走时遇见一辆公交车，走的途中遇见10辆，到甲时，刚好一辆公交车又要出发，这人走了多少分钟？
<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<gadget id="calculator">11 * 5</gadget>
<output>55</output>

<gadget id="calculator">55 - 15</gadget>
<output>40</output>

<result>40</result>