a-a a-b a-c aaa aab aac aae aak aao aas ab- aba abb abc abe abk abo abs ac- aca acb acc ace ack aco acs aea aeb aec aee aek aeo aes aka akb akc ake akk ako aks aoa aob aoc aoe aok aoo aos as- asa asb asc ase ask aso ass baa bab bac bae bak bao bas bba bbb bbc bbe bbk bbo bbs bca bcb bcc bce bck bco bcs be- bea beb bec bee bek beo bes bka bkb bkc bke bkk bko bks boa bob boc boe bok boo bos bsa bsb bsc bse bsk bso bss c-- caa cab cac cae cak cao cas cba cbb cbc cbe cbk cbo cbs cca ccb ccc cce cck cco ccs ce- cea ceb cec cee cek ceo ces cka ckb ckc cko cks co- coa cob coc coe cok coo cos csa csb csc cse csk cso css eaa eab eac eae eak eao eas eba ebb ebc ebe ebk ebo ebs ec- eca ecb ecc ece eck eco ecs eea eeb eec eee eek eeo ees eka ekb ekc eke eko eks eo- eoa eob eoc eoe eok eoo eos es- esa esb esc ese esk eso ess ka- kaa kab kac kae kak kao kas kba kbb kbc kbe kbk kbo kbs kca kcb kcc kce kck kcs ke- kea keb kec kee kek keo kes kkb kkc kke kkk kks koa kob koc koe kok koo kos ksa ksb ksc kse ksk kso kss oaa oab oac oae oak oao oas ob- oba obb obc obe obk obo obs oc- oca ocb occ ock oco ocs oea oeb oec oee oeo oes oka okb okc oke okk oko oks oo- ooa oob ooc ook ooo oos os- osa osb osc ose osk oso oss saa sab sac sae sak sao sas sba sbb sbc sbe sbk sbo sbs sca scb scc sce sck sco scs se- sea seb sec see sek seo ses sk- ska skb skc ske skk sko sks soa sob soc soe sok soo sos ss- ssa ssb ssc sse ssk sso sss