Ali Baba and the $40$ thieves want to cross Bosporus strait. They made a line so that any two people standing next to each other are friends. Ali Baba is the first, he is also a friend with the thief next to his neighbour. There is a single boat that can carry $2$ or $3$ people and these people must be friends. Can Ali Baba and the $40$ thieves always cross the strait if a single person cannot sail?