fff ffk ffo ffp ffs fkf fkk fkp fof fok foo fop fos fpk fpo fpp fps fsf fsk fso fsp fss kff kfo kfs kkk kkp kks kof kok koo kop kos kpf kpk kpo kpp kps ksf ksk kso ksp kss of- off ofo ofp ofs okk oko okp oks oo- oof ook ooo oop oos op- opf opk opo opp ops os- osf osk oso osp oss p-p pff pfk pfo pfp pfs pkf pko pkp pks pof pok poo pop pos ppf ppk ppo ppp pps ps- psf psk pso psp pss sff sfk sfo sfp sfs sk- skf skk sko skp sks sof sok soo sop sos spf spk spo spp sps ss- ssf ssk sso ssp sss