a-a a-b a-c aaa aab aac aae aak aan ab- aba abb abc abe abk abn ac- aca acb acc ace ack acn aea aeb aec aee aek aen aka akb akc ake akk akn an- ana anb anc ane ank ann baa bab bac bae bak ban bba bbb bbc bbe bbk bbn bca bcb bcc bce bck bcn be- bea beb bec bee bek ben bka bkb bkc bke bkk bkn bna bnb bnc bne bnk bnn c-- caa cab cac cae cak can cba cbb cbc cbe cbk cbn cca ccb ccc cce cck ccn ce- cea ceb cec cee cek cen cka ckb ckc cn- cna cnb cnc cne cnn eaa eab eac eae eak ean eba ebb ebc ebe ebk ebn ec- eca ecb ecc ece eck ecn eea eeb eec eee eek een eka ekb ekc eke en- ena enb enc ene enk enn ka- kaa kab kac kae kak kan kba kbb kbc kbe kbk kbn kca kcb kcc kce kck kcn ke- kea keb kec kee kek ken kkb kkc kke kkk kkn kn- kna knc kne knk knn naa nab nac nae nak nan nba nbb nbc nbe nbk nbn nca ncb ncc nce nck ncn ne- nea neb nec nee nek nen nka nkc nke nkk nkn nna nnb nnc nne nnk nnn