a-a a-b a-c aaa aab aac aae aaf aak aao ab- aba abb abc abe abf abk abo ac- aca acb acc ace acf ack aco aea aeb aec aee aef aek aeo af- afa afb afc afe aff afk afo aka akb akc ake akk ako aoa aob aoc aoe aof aok aoo baa bab bac bae baf bak bao bba bbb bbc bbe bbf bbk bbo bca bcb bcc bce bcf bck bco be- bea beb bec bee bef bek beo bfa bfb bfc bfe bff bfo bka bkb bkc bke bkf bkk bko boa bob boc boe bof bok boo c-- caa cab cac cae caf cak cao cba cbb cbc cbe cbf cbk cbo cca ccb ccc cce ccf cck cco ce- cea ceb cec cee cef cek ceo cfa cfb cfc cfe cff cfk cfo cka ckb ckc cko co- coa cob coc coe cof cok coo eaa eab eac eae eaf eak eao eba ebb ebc ebe ebf ebk ebo ec- eca ecb ecc ece ecf eck eco eea eeb eec eee eef eek eeo ef- efa efb efc efe eff efo eka ekb ekc eke ekf eko eo- eoa eob eoc eoe eof eok eoo faa fab fac fae faf fak fao fba fbb fbc fbe fbf fbk fbo fca fcb fcc fce fcf fck fco fea feb fec fee fef fek feo ffa ffc ffe fff ffk ffo fka fkb fkc fkf fkk foa fob foc foe fof fok foo ka- kaa kab kac kae kaf kak kao kba kbb kbc kbe kbf kbk kbo kca kcb kcc kce kck ke- kea keb kec kee kef kek keo kfa kfc kff kfo kkb kkc kke kkk koa kob koc koe kof kok koo oaa oab oac oae oaf oak oao ob- oba obb obc obe obf obk obo oc- oca ocb occ ocf ock oco oea oeb oec oee oef oeo of- ofa ofb ofc ofe off ofo oka okb okc oke okk oko oo- ooa oob ooc oof ook ooo