a-a a-b a-c aaa aab aac aan aao ab- aba abb abc abn abo ac- aca acb acc acn aco an- ana anb anc ann ano aoa aob aoc aon aoo baa bab bac ban bao bba bbb bbc bbn bbo bca bcb bcc bcn bco bna bnb bnc bnn bno boa bob boc bon boo c-- caa cab cac can cao cba cbb cbc cbn cbo cca ccb ccc ccn cco cn- cna cnb cnc cnn cno co- coa cob coc con coo naa nab nac nan nao nba nbb nbc nbn nbo nca ncb ncc ncn nco nna nnb nnc nnn nno no- noa nob noc non noo oaa oab oac oan oao ob- oba obb obc obn obo oc- oca ocb occ ocn oco on- ona onb onc onn ono oo- ooa oob ooc oon ooo