Three missionaries and three cannibals stand on the bank of a river that they wish to cross. There is a boat available which can ferry up to two people across. The goal is to find a schedule for ferrying all the cannibals and all the missionaries safely across the river. The constraint is that, if at any point the cannibals outnumber the missionaries on either bank, the cannibals will eat the missionaries. Note that the boat cannot cross the river by itself with no people on board.