a-a a-b a-c aaa aab aac aao aas ab- aba abb abc abo abs ac- aca acb acc aco acs aoa aob aoc aoo aos as- asa asb asc aso ass baa bab bac bao bas bba bbb bbc bbo bbs bca bcb bcc bco bcs boa bob boc boo bos bsa bsb bsc bso bss c-- caa cab cac cao cas cba cbb cbc cbo cbs cca ccb ccc cco ccs co- coa cob coc coo cos csa csb csc cso css oaa oab oac oao oas ob- oba obb obc obo obs oc- oca ocb occ oco ocs oo- ooa oob ooc ooo oos os- osa osb osc oso oss saa sab sac sao sas sba sbb sbc sbo sbs sca scb scc sco scs soa sob soc soo sos ss- ssa ssb ssc sso sss