a-a a-b a-c aaa aab aac aad aak aao ab- aba abb abc abd abk abo ac- aca acb acc acd ack aco ad- ada adb adc add adk ado aka akb akc akd akk ako aoa aob aoc aod aok aoo baa bab bac bad bak bao bba bbb bbc bbd bbk bbo bca bcb bcc bcd bck bco bda bdb bdc bdd bdk bdo bka bkb bkc bkk bko boa bob boc bod bok boo c-- caa cab cac cad cak cao cba cbb cbc cbd cbk cbo cca ccb ccc ccd cck cco cda cdb cdc cdd cdk cdo cka ckb ckc ckd cko co- coa cob coc cod cok coo daa dab dac dad dak dao dba dbb dbc dbd dbk dbo dca dcb dcc dcd dck dco dda ddb ddc ddd ddk ddo dka dkb dkc dkk dko doa dob doc dod dok doo ka- kaa kab kac kad kak kao kba kbb kbc kbd kbk kbo kca kcb kcc kcd kck kda kdb kdc kdk kdo kkb kkc kkk koa kob koc kod kok koo oaa oab oac oad oak oao ob- oba obb obc obd obk obo oc- oca ocb occ ocd ock oco oda odb odc odd odo oka okb okc okd okk oko oo- ooa oob ooc ood ook ooo