Indiana Jones and his party need to cross a flimsy rope bridge over a mile-deep gorge. It is so dark that it is impossible to cross the bridge without a flashlight. Furthermore, the bridge is so flimsy that it can only support the weight of two people at once. The party has a single flashlight, which has a weak beam, so that whenever two people cross the bridge they are constrained to walk together, at the speed of the slower person. Indiana Jones can cross the bridge in 5 minutes; his girlfriend can cross it in 10 minutes; his father needs 20 minutes and his father's sidekick needs 25 minutes to cross. Finally, they must all reach the other side within one hour. Is it possible for them to achieve this?