On a dark night, there are four people A, B, C, and D who want to cross a bridge, and they only have one flashlight. At most two people can cross the bridge at the same time at the same time, and there must be flashlights when crossing the bridge, so Someone needs to bring a flashlight back and forth between the two ends of the bridge. The flashlight cannot be passed by throwing it. Four people walk at different speeds. If two people walk together, the slower speed shall prevail. It is known that the time for A, B, C, and D to cross the bridge is 2 minutes, 3 minutes, 7 minutes, and 10 minutes respectively. How do you arrange for them all to cross the bridge in the shortest time? How many minutes is this minimum time?
在一个漆黑的晚上，有甲、乙、丙、丁四人要经过一座桥，而他们只有一只手电筒，一次同时最多可以有两人一起过桥，而过桥的时候必须有手电，所以就要有人把手电筒带来带去，来回于桥的两端．手电筒不能用丢的方式来传递．四人步行的速度不同，若两人同行，则以较慢者的速度为准．已知甲、乙、丙、丁四人过桥的时间分别是2分钟，3分钟，7分钟，十分钟，你怎样安排他们在最短的时间内全部过桥？这个最短时间是多少分钟？
<gadget id="calculator">3 + 2 + 10 + 3 + 3</gadget>
<output>21</output>

<result>21</result>