There is only one barber in the barber room. It takes 20 minutes for Xiaohua to get a flat haircut, 40 minutes for Xiaoli to dye her hair, and 15 minutes for Grandpa to get a haircut. To minimize the total waiting time of the three people, how should the sequence of haircuts be arranged?
理发室里只有一个理发师，小华理平头要20分钟，小丽染发要40分钟，爷爷理发要15分钟，要使3人的等候时间总和最少，应该如何安排理发顺序？
<gadget id="calculator">15 * 3</gadget>
<output>45</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 * 1</gadget>
<output>40</output>

<gadget id="calculator">45 + 40 + 40</gadget>
<output>125</output>

<result>125</result>