a-a a-b a-c aaa aab aac aad aak aao aas ab- aba abb abc abd abk abo abs ac- aca acb acc acd ack aco acs ad- ada adb adc add adk ado ads aka akb akc akd akk ako aks aoa aob aoc aod aok aoo aos as- asa asb asc asd ask aso ass baa bab bac bad bak bao bas bba bbb bbc bbd bbk bbo bbs bca bcb bcc bcd bck bco bcs bda bdb bdc bdd bdk bdo bds bka bkb bkc bkk bko bks boa bob boc bod bok boo bos bsa bsb bsc bsd bsk bso bss c-- caa cab cac cad cak cao cas cba cbb cbc cbd cbk cbo cbs cca ccb ccc ccd cck cco ccs cda cdb cdc cdd cdk cdo cds cka ckb ckc ckd cko cks co- coa cob coc cod cok coo cos csa csb csc csd csk cso css daa dab dac dad dak dao das dba dbb dbc dbd dbk dbo dbs dca dcb dcc dcd dck dco dcs dda ddb ddc ddd ddk ddo dds dka dkb dkc dkk dko dks doa dob doc dod dok doo dos dsa dsb dsc dsd dsk dso dss ka- kaa kab kac kad kak kao kas kba kbb kbc kbd kbk kbo kbs kca kcb kcc kcd kck kcs kda kdb kdc kdk kdo kds kkb kkc kkk kks koa kob koc kod kok koo kos ksa ksb ksc ksd ksk kso kss oaa oab oac oad oak oao oas ob- oba obb obc obd obk obo obs oc- oca ocb occ ocd ock oco ocs oda odb odc odd odo ods oka okb okc okd okk oko oks oo- ooa oob ooc ood ook ooo oos os- osa osb osc osd osk oso oss saa sab sac sad sak sao sas sba sbb sbc sbd sbk sbo sbs sca scb scc scd sck sco scs sda sdb sdc sdd sdk sdo sds sk- ska skb skc skd skk sko sks soa sob soc sod sok soo sos ss- ssa ssb ssc ssd ssk sso sss