a-a a-b aaa aab aae aaf aao aas ab- aba abb abe abf abo abs aea aeb aee aef aeo aes af- afa afb afe aff afo afs aoa aob aoe aof aoo aos as- asa asb ase asf aso ass baa bab bae baf bao bas bba bbb bbe bbf bbo bbs be- bea beb bee bef beo bes bfa bfb bfe bff bfo bfs boa bob boe bof boo bos bsa bsb bse bsf bso bss eaa eab eae eaf eao eas eba ebb ebe ebf ebo ebs eea eeb eee eef eeo ees ef- efa efb efe eff efo efs eo- eoa eob eoe eof eoo eos es- esa esb ese esf eso ess faa fab fae faf fao fas fba fbb fbe fbf fbo fbs fea feb fee fef feo fes ffa ffe fff ffo ffs foa fob foe fof foo fos fsa fsb fse fsf fso fss oaa oab oae oaf oao oas ob- oba obb obe obf obo obs oea oeb oee oef oeo oes of- ofa ofb ofe off ofo ofs oo- ooa oob oof ooo oos os- osa osb ose osf oso oss saa sab sae saf sao sas sba sbb sbe sbf sbo sbs se- sea seb see sef seo ses sfa sfb sfe sff sfo sfs soa sob soe sof soo sos ss- ssa ssb sse ssf sso sss