Three soldiers (s1, hs, s3) want to cross a river.  Two boys (b1 and b2) have a boat on the same side of the river.  However, the boat can carry only the two boys or one solder at a time.  To win the game, a player must find a schedule of crossings that gets all three soldiers across the river and leave the boat with the two boys on the original bank by step 12.