a-a a-b a-c aaa aab aac aak aan aax ab- aba abb abc abk abn abx ac- aca acb acc ack acn acx aka akb akc akk akn an- ana anb anc ank ann anx ax- axa axk axn axx baa bab bac bak ban bax bba bbb bbc bbk bbn bbx bca bcb bcc bck bcn bcx bka bkb bkc bkk bkn bkx bna bnb bnc bnk bnn bnx bxb bxn bxx c-- caa cab cac cak can cax cba cbb cbc cbk cbn cbx cca ccb ccc cck ccn ccx cka ckb ckc ckx cn- cna cnb cnc cnn cnx cxc cxk cxx ka- kaa kab kac kak kan kax kba kbb kbc kbk kbn kbx kca kcb kcc kck kcn kcx kkb kkc kkk kkn kn- kna knc knk knn knx naa nab nac nak nan nax nba nbb nbc nbk nbn nbx nca ncb ncc nck ncn ncx nka nkc nkk nkn nna nnb nnc nnk nnn nxc xaa xac xak xan xbc xbx xcb xcx xkb xna xnc xnk xxx