program for bridge and torch problem

A group of K persons want to cross a bridge from East to West during the night. The persons that are crossing the bridge must use a flashlight. There is only one flashlight. The bridge is very narrow and allows two persons to cross it at the same time at most. Two persons go from east to west and one person returns with the flashlight from west to east. If the two persons are crossing the bridge together, they are crossing it at the speed of the slower one. These people are trying to cross the bridge as quickly as possible.