a-a a-b a-c aaa aab aac aae aak ab- aba abb abc abe abk ac- aca acb acc ace ack aea aeb aec aee aek aka akb akc ake akk baa bab bac bae bak bba bbb bbc bbe bbk bca bcb bcc bce bck be- bea beb bec bee bek bka bkb bkc bke bkk c-- caa cab cac cae cak cba cbb cbc cbe cbk cca ccb ccc cce cck ce- cea ceb cec cee cek cka ckb ckc eaa eab eac eae eak eba ebb ebc ebe ebk ec- eca ecb ecc ece eck eea eeb eec eee eek eka ekb ekc eke ka- kaa kab kac kae kak kba kbb kbc kbe kbk kca kcb kcc kce kck ke- kea keb kec kee kek kkb kkc kke kkk