a-a a-b a-c aaa aab aac aad aao aas ab- aba abb abc abd abo abs ac- aca acb acc acd aco acs ad- ada adb adc add ado ads aoa aob aoc aod aoo aos as- asa asb asc asd aso ass baa bab bac bad bao bas bba bbb bbc bbd bbo bbs bca bcb bcc bcd bco bcs bda bdb bdc bdd bdo bds boa bob boc bod boo bos bsa bsb bsc bsd bso bss c-- caa cab cac cad cao cas cba cbb cbc cbd cbo cbs cca ccb ccc ccd cco ccs cda cdb cdc cdd cdo cds co- coa cob coc cod coo cos csa csb csc csd cso css daa dab dac dad dao das dba dbb dbc dbd dbo dbs dca dcb dcc dcd dco dcs dda ddb ddc ddd ddo dds doa dob doc dod doo dos dsa dsb dsc dsd dso dss oaa oab oac oad oao oas ob- oba obb obc obd obo obs oc- oca ocb occ ocd oco ocs oda odb odc odd odo ods oo- ooa oob ooc ood ooo oos os- osa osb osc osd oso oss saa sab sac sad sao sas sba sbb sbc sbd sbo sbs sca scb scc scd sco scs sda sdb sdc sdd sdo sds soa sob soc sod soo sos ss- ssa ssb ssc ssd sso sss