a-a a-b aaa aab aae aao aas ab- aba abb abe abo abs aea aeb aee aeo aes aoa aob aoe aoo aos as- asa asb ase aso ass baa bab bae bao bas bba bbb bbe bbo bbs be- bea beb bee beo bes boa bob boe boo bos bsa bsb bse bso bss eaa eab eae eao eas eba ebb ebe ebo ebs eea eeb eee eeo ees eo- eoa eob eoe eoo eos es- esa esb ese eso ess oaa oab oae oao oas ob- oba obb obe obo obs oea oeb oee oeo oes oo- ooa oob ooo oos os- osa osb ose oso oss saa sab sae sao sas sba sbb sbe sbo sbs se- sea seb see seo ses soa sob soe soo sos ss- ssa ssb sse sso sss