a-ak aaaa aaab aaac aaad aaba aabb aabc aabd aaca aacb aacc aacd aack aada aadc aaka abaa abab abac abad abak abb- abba abbb abca abcb abcc abcd abda acaa acab acac acad acba acca accc accd acda acdb acdc ackd adaa adab adac adad adak adba adbc adcc adda addc addd akaa akca akka baaa baad baak baba babb bac- baca bacc back bada badb badd bak- baka bbad bbbb bbdd bcaa bcbc bcca bccc bcda bdbc bddc c-cd caaa caab caac caba cac- caca cacc cack cada cadc cadd caka cbac cbbc cbca cbcc cbdb cbdc cbka ccaa ccab ccac ccad ccba ccbc ccca cccb cccc ccdc cdaa cdac cdad cdba cdda cddb ckac ckbc ckck daab daad daba dabb daca dada daka dbcc dcbc dcca dccb dccc dcdb dddd dkba dkdc kaaa kaab kaak kaba kabb kabc kabd kacb kacc kacd kad- kada kadd kaka kakc kakk kbaa kbab kbac kbad kbak kbba kbbb kbbc kbbd kbbk kbca kbcb kbck kbdb kbkb kbkk kcaa kcab kcac kcad kcba kcbc kcbd kcbk kcca kccb kccc kccd kcck kcda kcdc kcdd kckc kckk kdaa kdab kdac kdad kdak kdbb kdca kdcc kdcd kddb kddc kddd kddk kdka kdkb kdkd kdkk kkaa kkac kkba kkbb kkbd kkcb kkcd kkck kkda kkdc kkdd kkkk