有一m*n的棋盘(即棋盘由m行和n列)，一马放在棋盘中任意位置，马按中国象棋跳法，从初始位置起跳，跳至边界后返回，求所有能返回初始位置的周游路线。(A m*n board (the board consists of M rows and N columns), a horse placed anywhere in the board, according to the China chess horse jump method, from the initial position jump, jump to the border after the return, all can return to the initial position of the travel route.)