a-a a-b a-c aaa aab aac aak aan aao aas ab- aba abb abc abk abn abo abs ac- aca acb acc ack acn aco acs aka akb akc akk akn ako aks an- ana anb anc ank ann ano ans aoa aob aoc aok aon aoo aos as- asa asb asc ask asn aso ass baa bab bac bak ban bao bas bba bbb bbc bbk bbn bbo bbs bca bcb bcc bck bcn bco bcs bka bkb bkc bkk bkn bko bks bna bnb bnc bnk bnn bno bns boa bob boc bok bon boo bos bsa bsb bsc bsk bsn bso bss c-- caa cab cac cak can cao cas cba cbb cbc cbk cbn cbo cbs cca ccb ccc cck ccn cco ccs cka ckb ckc cko cks cn- cna cnb cnc cnn cno cns co- coa cob coc cok con coo cos csa csb csc csk csn cso css ka- kaa kab kac kak kan kao kas kba kbb kbc kbk kbn kbo kbs kca kcb kcc kck kcn kcs kkb kkc kkk kkn kks kn- kna knc knk knn kno koa kob koc kok kon koo kos ksa ksb ksc ksk ksn kso kss naa nab nac nak nan nao nas nba nbb nbc nbk nbn nbo nbs nca ncb ncc nck ncn nco ncs nka nkc nkk nkn nko nks nna nnb nnc nnk nnn nno nns no- noa nob noc nok non noo nos nsa nsb nsc nsk nsn nso nss oaa oab oac oak oan oao oas ob- oba obb obc obk obn obo obs oc- oca ocb occ ock ocn oco ocs oka okb okc okk oko oks on- ona onb onc onk onn ono ons oo- ooa oob ooc ook oon ooo oos os- osa osb osc osk osn oso oss saa sab sac sak san sao sas sba sbb sbc sbk sbn sbo sbs sca scb scc sck scn sco scs sk- ska skb skc skk sko sks sna snb snc snk snn sno sns soa sob soc sok son soo sos ss- ssa ssb ssc ssk ssn sso sss