a-a a-b a-c aaa aab aac aae aaf aak aan aao ab- aba abb abc abe abf abk abn abo ac- aca acb acc ace acf ack acn aco aea aeb aec aee aef aek aen aeo af- afa afb afc afe aff afk afn afo aka akb akc ake akk akn ako an- ana anb anc ane anf ank ann ano aoa aob aoc aoe aof aok aon aoo baa bab bac bae baf bak ban bao bba bbb bbc bbe bbf bbk bbn bbo bca bcb bcc bce bcf bck bcn bco be- bea beb bec bee bef bek ben beo bfa bfb bfc bfe bff bfn bfo bka bkb bkc bke bkf bkk bkn bko bna bnb bnc bne bnf bnk bnn bno boa bob boc boe bof bok bon boo c-- caa cab cac cae caf cak can cao cba cbb cbc cbe cbf cbk cbn cbo cca ccb ccc cce ccf cck ccn cco ce- cea ceb cec cee cef cek cen ceo cfa cfb cfc cfe cff cfk cfn cfo cka ckb ckc cko cn- cna cnb cnc cne cnf cnn cno co- coa cob coc coe cof cok con coo eaa eab eac eae eaf eak ean eao eba ebb ebc ebe ebf ebk ebn ebo ec- eca ecb ecc ece ecf eck ecn eco eea eeb eec eee eef eek een eeo ef- efa efb efc efe eff efo eka ekb ekc eke ekf eko en- ena enb enc ene enf enk enn eno eo- eoa eob eoc eoe eof eok eon eoo faa fab fac fae faf fak fan fao fba fbb fbc fbe fbf fbk fbn fbo fca fcb fcc fce fcf fck fcn fco fea feb fec fee fef fek fen feo ffa ffc ffe fff ffk ffn ffo fka fkb fkc fkf fkk fna fnb fnc fne fnf fnk fnn foa fob foc foe fof fok fon foo ka- kaa kab kac kae kaf kak kan kao kba kbb kbc kbe kbf kbk kbn kbo kca kcb kcc kce kck kcn ke- kea keb kec kee kef kek ken keo kfa kfc kff kfo kkb kkc kke kkk kkn kn- kna knc kne knf knk knn kno koa kob koc koe kof kok kon koo naa nab nac nae naf nak nan nao nba nbb nbc nbe nbf nbk nbn nbo nca ncb ncc nce ncf nck ncn nco ne- nea neb nec nee nef nek nen neo nfa nfb nfc nfe nff nfk nfn nfo nka nkc nke nkf nkk nkn nko nna nnb nnc nne nnf nnk nnn nno no- noa nob noc noe nof nok non noo oaa oab oac oae oaf oak oan oao ob- oba obb obc obe obf obk obn obo oc- oca ocb occ ocf ock ocn oco oea oeb oec oee oef oen oeo of- ofa ofb ofc ofe off ofn ofo oka okb okc oke okk oko on- ona onb onc one onf onk onn ono oo- ooa oob ooc oof ook oon ooo