a-a a-b a-c aaa aab aac aao aas aax ab- aba abb abc abo abs abx ac- aca acb acc aco acs acx aoa aob aoc aoo aos aox as- asa asb asc aso ass asx ax- axa axo axs axx baa bab bac bao bas bax bba bbb bbc bbo bbs bbx bca bcb bcc bco bcs bcx boa bob boc boo bos box bsa bsb bsc bso bss bsx bxb bxo bxx c-- caa cab cac cao cas cax cba cbb cbc cbo cbs cbx cca ccb ccc cco ccs ccx co- coa cob coc coo cos cox csa csb csc cso css csx cxc cxo cxs cxx oaa oab oac oao oas oax ob- oba obb obc obo obs obx oc- oca ocb occ oco ocs ocx oo- ooa oob ooc ooo oos oox os- osa osb osc oso oss osx ox- oxa oxb oxc oxo oxx saa sab sac sao sas sax sba sbb sbc sbo sbs sbx sca scb scc sco scs scx soa sob soc soo sos sox ss- ssa ssb ssc sso sss ssx sxc sxs xaa xac xas xbc xbx xcb xcx xoa xoc xoo xos xox xsa xsb xsc xss xxo xxx