a man takes a NAME_1, a sheep, and a cabbage to the riverside and wants to cross the river with the only boat. he can take only one item with him on the boat each time. he cannot leave the NAME_1 and sheep on either side of the river at the same time, because the NAME_1 would eat the sheep. he cannot leave the sheep and cabbage on either side of the river at the same time, because the sheep would eat the cabbage. now the question is, at least how many times the man needs to cross the river in order to have all three items moved to the other side of the river? 