a-a a-b a-c aaa aab aac aao aas aay ab- aba abb abc abo abs aby ac- aca acb acc aco acs acy aoa aob aoc aoo aos as- asa asb asc aso ass asy ay- aya ayc ayo ays baa bab bac bao bas bay bba bbb bbc bbo bbs bby bca bcb bcc bco bcs bcy boa bob boc boo bos boy bsa bsb bsc bso bss bsy by- bya byc byo bys c-- caa cab cac cao cas cay cba cbb cbc cbo cbs cby cca ccb ccc cco ccs co- coa cob coc coo cos coy csa csb csc cso css csy cya cyb cyc cyo cys oaa oab oac oao oas ob- oba obb obc obo obs oby oc- oca ocb occ oco ocs oo- ooa oob ooc ooo oos os- osa osb osc oso oss oya oyo oys saa sab sac sao sas say sba sbb sbc sbo sbs sby sca scb scc sco scs soa sob soc soo sos soy ss- ssa ssb ssc sso sss sy- sya syb syc sys yaa yab yac yao yas yay ybc ybs yby yca ycc yco ycs ycy yob yoc yoo yos yoy ysa ysb ysc yso yss ysy yyb yyc yys yyy