a-a a-b a-c aaa aab aac aad aak aas ab- aba abb abc abd abk abs ac- aca acb acc acd ack acs ad- ada adb adc add adk ads aka akb akc akd akk aks as- asa asb asc asd ask ass baa bab bac bad bak bas bba bbb bbc bbd bbk bbs bca bcb bcc bcd bck bcs bda bdb bdc bdd bdk bds bka bkb bkc bkk bks bsa bsb bsc bsd bsk bss c-- caa cab cac cad cak cas cba cbb cbc cbd cbk cbs cca ccb ccc ccd cck ccs cda cdb cdc cdd cdk cds cka ckb ckc ckd cks csa csb csc csd csk css daa dab dac dad dak das dba dbb dbc dbd dbk dbs dca dcb dcc dcd dck dcs dda ddb ddc ddd ddk dds dka dkb dkc dkk dks dsa dsb dsc dsd dsk dss ka- kaa kab kac kad kak kas kba kbb kbc kbd kbk kbs kca kcb kcc kcd kck kcs kda kdb kdc kdk kds kkb kkc kkk kks ksa ksb ksc ksd ksk kss saa sab sac sad sak sas sba sbb sbc sbd sbk sbs sca scb scc scd sck scs sda sdb sdc sdd sdk sds sk- ska skb skc skd skk sks ss- ssa ssb ssc ssd ssk sss