a-a a-b a-c aaa aab aac aae aaf aao ab- aba abb abc abe abf abo ac- aca acb acc ace acf aco aea aeb aec aee aef aeo af- afa afb afc afe aff afo aoa aob aoc aoe aof aoo baa bab bac bae baf bao bba bbb bbc bbe bbf bbo bca bcb bcc bce bcf bco be- bea beb bec bee bef beo bfa bfb bfc bfe bff bfo boa bob boc boe bof boo c-- caa cab cac cae caf cao cba cbb cbc cbe cbf cbo cca ccb ccc cce ccf cco ce- cea ceb cec cee cef ceo cfa cfb cfc cfe cff cfo co- coa cob coc coe cof coo eaa eab eac eae eaf eao eba ebb ebc ebe ebf ebo ec- eca ecb ecc ece ecf eco eea eeb eec eee eef eeo ef- efa efb efc efe eff efo eo- eoa eob eoc eoe eof eoo faa fab fac fae faf fao fba fbb fbc fbe fbf fbo fca fcb fcc fce fcf fco fea feb fec fee fef feo ffa ffc ffe fff ffo foa fob foc foe fof foo oaa oab oac oae oaf oao ob- oba obb obc obe obf obo oc- oca ocb occ ocf oco oea oeb oec oee oef oeo of- ofa ofb ofc ofe off ofo oo- ooa oob ooc oof ooo