a-a a-b a-c aaa aab aac aae aaf aak ab- aba abb abc abe abf abk ac- aca acb acc ace acf ack aea aeb aec aee aef aek af- afa afb afc afe aff afk aka akb akc ake akk baa bab bac bae baf bak bba bbb bbc bbe bbf bbk bca bcb bcc bce bcf bck be- bea beb bec bee bef bek bfa bfb bfc bfe bff bka bkb bkc bke bkf bkk c-- caa cab cac cae caf cak cba cbb cbc cbe cbf cbk cca ccb ccc cce ccf cck ce- cea ceb cec cee cef cek cfa cfb cfc cfe cff cfk cka ckb ckc eaa eab eac eae eaf eak eba ebb ebc ebe ebf ebk ec- eca ecb ecc ece ecf eck eea eeb eec eee eef eek ef- efa efb efc efe eff eka ekb ekc eke ekf faa fab fac fae faf fak fba fbb fbc fbe fbf fbk fca fcb fcc fce fcf fck fea feb fec fee fef fek ffa ffc ffe fff ffk fka fkb fkc fkf fkk ka- kaa kab kac kae kaf kak kba kbb kbc kbe kbf kbk kca kcb kcc kce kck ke- kea keb kec kee kef kek kfa kfc kff kkb kkc kke kkk