bbbb bbbs bffs bfsi bfsr bfts bftt bibb bibi bibs biff bifi biis birb biri birr birs birt bis- biss bist bits bitt bris brit brrr brrs brsb brsr brst bsff bsfs bsts btrt btss bttb fbis fbrs ffff ffii ffrr ffss fftf fibs fiff fifi fift fiii firs fisi fiss fist fiti fits fitt frib fris frit frsb frst fsfi fssf ftii ftrs ftsr ibfi ibis ibri ibsf ibss ibtb ibts ifbb ifis ifit ifrb ifrf ifri ifsb iiii iiis iiit iirs iisi iisr iist iitr iitt iri- iris irri irrs irsf irtf irti irts isbt isis isit isri issf issi issr isss isti istr ists itbs itif itis itrf itri itrs itsf itsi ittf rbbb rbbr rbbs rbis rbss rbst rib- ribs riff rifs rift riif riis riri rirs risi riss rist riti rits ritt rrif rrrr rsbi rsis rsts rtbf rtfb rtss rtts s-ib s-ii sbbs sbsi sbst sfss sfts sibi sibs siff sifr sift siit sirf siri sirr sirs sirt sisi siss sist sit- siti sits sitt srfi srib sris srtr ssbr ssis ssit ssri ssrs sssb sssf sssi ssss sstb ssts stbs stib stif stir stis stit stri strs stsf stsi stss sttr tbbs tbit tbrb tbst tfrs tfsi tfss tibi tibs tiff tift tiit tirb tiri tirr tirs tisb tisi tiss tist titi tits titt trfr tri- trib trif tris trit trsi trst trtr tsis tssf tssi tssr tsst tsts ttbb ttff ttss tttt