a-a a-b aaa aab aan aao aas ab- aba abb abn abo abs an- ana anb ann ano ans aoa aob aon aoo aos as- asa asb asn aso ass baa bab ban bao bas bba bbb bbn bbo bbs bna bnb bnn bno bns boa bob bon boo bos bsa bsb bsn bso bss naa nab nan nao nas nba nbb nbn nbo nbs nna nnb nnn nno nns no- noa nob non noo nos nsa nsb nsn nso nss oaa oab oan oao oas ob- oba obb obn obo obs on- ona onb onn ono ons oo- ooa oob oon ooo oos os- osa osb osn oso oss saa sab san sao sas sba sbb sbn sbo sbs sna snb snn sno sns soa sob son soo sos ss- ssa ssb ssn sso sss