Four people are trying to cross a sketchy rope bridge in the middle of the night. Only two can cross at a time. They only have one flashlight, and so one person must bring it back across the bridge to the starting side before anyone else can cross. One person takes 1 minute to cross, another takes 2 minutes to cross, another takes 5 minutes to cross, and the last person takes 10 minutes to cross. Hypothetically, if the 2-minute person and the 5-minute person crossed together, that would take a total of 5 minutes (but someone needs to bring the flashlight back, resulting in 7 minutes spent if the 2-minute person returns with the light). Everyone needs to get across in 17 minutes or less, otherwise they will be ripped apart and consumed by zombies.