Four people got lost in the woods and only managed to find the hanging bridge leading to the path back home after nightfall. From previous crossings, they know the bridge is unstable and can only support two people at a time. They also know that the single torch they've managed to fashion will be essential for whoever is crossing the bridge. The four individuals have different levels of fitness, so they'll each take different amounts of time in order reach the other side:

Person 1 = 5 min

Person 2 = 10 min

Person 3 = 20 min

Person 4 = 25 min

Whenever two are crossing together, they'll take as much time as the slowest one of them. How can they all make it across the bridge in 60 minutes?