a-a a-b a-c aaa aab aac aad aas ab- aba abb abc abd abs ac- aca acb acc acd acs ad- ada adb adc add ads as- asa asb asc asd ass baa bab bac bad bas bba bbb bbc bbd bbs bca bcb bcc bcd bcs bda bdb bdc bdd bds bsa bsb bsc bsd bss c-- caa cab cac cad cas cba cbb cbc cbd cbs cca ccb ccc ccd ccs cda cdb cdc cdd cds csa csb csc csd css daa dab dac dad das dba dbb dbc dbd dbs dca dcb dcc dcd dcs dda ddb ddc ddd dds dsa dsb dsc dsd dss saa sab sac sad sas sba sbb sbc sbd sbs sca scb scc scd scs sda sdb sdc sdd sds ss- ssa ssb ssc ssd sss