-er a-a a-b a-c aaa aab aac aae aan aao aar ab- aba abb abc abe abn abo abr ac- aca acb acc ace acn aco acr aea aeb aec aee aen aeo aer an- ana anb anc ane ann ano anr aoa aob aoc aoe aon aoo aor ar- ara arb arc are arn aro arr baa bab bac bae ban bao bar bba bbb bbc bbe bbn bbo bbr bca bcb bcc bce bcn bco bcr be- bea beb bec bee ben beo ber bna bnb bnc bne bnn bno bnr boa bob boc boe bon boo bor bra brb bre brn bro brr c-- caa cab cac cae can cao car cba cbb cbc cbe cbn cbo cbr cca ccb ccc cce ccn cco ccr ce- cea ceb cec cee cen ceo cer cn- cna cnb cnc cne cnn cno cnr co- coa cob coc coe con coo cor cra crb crc cre crn cro crr eaa eab eac eae ean eao ear eba ebb ebc ebe ebn ebo ebr ec- eca ecb ecc ece ecn eco ecr eea eeb eec eee een eeo eer en- ena enb enc ene enn eno enr eo- eoa eob eoc eoe eon eoo eor era erb erc ere ern ero err naa nab nac nae nan nao nar nba nbb nbc nbe nbn nbo nbr nca ncb ncc nce ncn nco ncr ne- nea neb nec nee nen neo ner nna nnb nnc nne nnn nno no- noa nob noc noe non noo nor nra nrb nrc nre nrn nro nrr oaa oab oac oae oan oao oar ob- oba obb obc obe obn obo obr oc- oca ocb occ ocn oco ocr oea oeb oec oee oen oeo oer on- ona onb onc one onn ono onr oo- ooa oob ooc oon ooo oor or- ora orb orc ore orn oro orr ra- raa rab rac rae ran rao rar rba rbb rbc rbe rbn rbo rbr rca rcb rcc rce rcn rco rcr re- rea reb rec ree ren reo rer rna rnb rnc rnn rno rnr roa rob roc roe ron roo ror rra rrb rrc rrn rrr