a-a a-b a-c aaa aab aac aae aaf aan aao ab- aba abb abc abe abf abn abo ac- aca acb acc ace acf acn aco aea aeb aec aee aef aen aeo af- afa afb afc afe aff afn afo an- ana anb anc ane anf ann ano aoa aob aoc aoe aof aon aoo baa bab bac bae baf ban bao bba bbb bbc bbe bbf bbn bbo bca bcb bcc bce bcf bcn bco be- bea beb bec bee bef ben beo bfa bfb bfc bfe bff bfn bfo bna bnb bnc bne bnf bnn bno boa bob boc boe bof bon boo c-- caa cab cac cae caf can cao cba cbb cbc cbe cbf cbn cbo cca ccb ccc cce ccf ccn cco ce- cea ceb cec cee cef cen ceo cfa cfb cfc cfe cff cfn cfo cn- cna cnb cnc cne cnf cnn cno co- coa cob coc coe cof con coo eaa eab eac eae eaf ean eao eba ebb ebc ebe ebf ebn ebo ec- eca ecb ecc ece ecf ecn eco eea eeb eec eee eef een eeo ef- efa efb efc efe eff efo en- ena enb enc ene enf enn eno eo- eoa eob eoc eoe eof eon eoo faa fab fac fae faf fan fao fba fbb fbc fbe fbf fbn fbo fca fcb fcc fce fcf fcn fco fea feb fec fee fef fen feo ffa ffc ffe fff ffn ffo fna fnb fnc fne fnf fnn foa fob foc foe fof fon foo naa nab nac nae naf nan nao nba nbb nbc nbe nbf nbn nbo nca ncb ncc nce ncf ncn nco ne- nea neb nec nee nef nen neo nfa nfb nfc nfe nff nfn nfo nna nnb nnc nne nnf nnn nno no- noa nob noc noe nof non noo oaa oab oac oae oaf oan oao ob- oba obb obc obe obf obn obo oc- oca ocb occ ocf ocn oco oea oeb oec oee oef oen oeo of- ofa ofb ofc ofe off ofn ofo on- ona onb onc one onf onn ono oo- ooa oob ooc oof oon ooo