Question

Word problem! please help =(
There are three cannibals, and three missionaries at the edge of the river. There is a small raft which can only carry two people. If at any time, there are more cannibals than missionaries on either side of the river, the cannibals will gang up and eat the missionaries. (staying on the boat is not on option; if the boat is on one side of the river, so anyone is on the boat) how can they cross the river without anyone being eaten?