a-a a-b a-c aaa aab aac aae aak aao ab- aba abb abc abe abk abo ac- aca acb acc ace ack aco aea aeb aec aee aek aeo aka akb akc ake akk ako aoa aob aoc aoe aok aoo baa bab bac bae bak bao bba bbb bbc bbe bbk bbo bca bcb bcc bce bck bco be- bea beb bec bee bek beo bka bkb bkc bke bkk bko boa bob boc boe bok boo c-- caa cab cac cae cak cao cba cbb cbc cbe cbk cbo cca ccb ccc cce cck cco ce- cea ceb cec cee cek ceo cka ckb ckc cko co- coa cob coc coe cok coo eaa eab eac eae eak eao eba ebb ebc ebe ebk ebo ec- eca ecb ecc ece eck eco eea eeb eec eee eek eeo eka ekb ekc eke eko eo- eoa eob eoc eoe eok eoo ka- kaa kab kac kae kak kao kba kbb kbc kbe kbk kbo kca kcb kcc kce kck ke- kea keb kec kee kek keo kkb kkc kke kkk koa kob koc koe kok koo oaa oab oac oae oak oao ob- oba obb obc obe obk obo oc- oca ocb occ ock oco oea oeb oec oee oeo oka okb okc oke okk oko oo- ooa oob ooc ook ooo