You need to pay 2.5 yuan for one parking (no more than 1 hour) in a car parking lot. If you park for more than 1 hour, you need to pay 1.5 yuan for every 0.5 hours. Less than 0.5 hours are counted as 0.5 hours, and Uncle Zhang paid 8.5 yuan. How long has his car been parked for at least?
在一个汽车停车场停车一次(不超过1小时)需要交费2.5元，如果停车超过1小时，超过部分，每0.5小时要交1.5元．不足0.5小时按0.5小时算，张叔叔交了8.5元，他的车至少停了多长时间？
<gadget id="calculator">8.5 - 2.5</gadget>
<output>6</output>

<gadget id="calculator">1.5 + 1.5</gadget>
<output>3</output>

<gadget id="calculator">6 / 3</gadget>
<output>2</output>

<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<result>3</result>