Alice, Bob, Charlie, and Daniel need to get across a river. The only way to cross the river is by an old wooden bridge, which holds at most two people at a time. Because it is dark, they can't cross the bridge without a lantern, of which they only have one. Each pair can only walk at the speed of the slower person. They need to get all of them across to the other side as quickly as possible. Alice takes 10 minutes to cross; Bob takes 5 minutes; Charlie takes 2 minutes; Daniel takes 1 minute. What is the minimum time to get all of them across to the other side?
