bbbb bbbs bffs bfsi bfts bftt bibb bibi bibs biff bifi biis bis- biss bist bits bitt bsff bsfs bsts btss bttb fbis ffff ffii ffss fftf fibs fiff fifi fift fiii fisi fiss fist fiti fits fitt fsfi fssf ftii ibfi ibis ibsf ibss ibtb ibts ifbb ifis ifit ifsb iiii iiis iiit iisi iist iitt isbt isis isit issf issi isss isti ists itbs itif itis itsf itsi ittf s-ib s-ii sbbs sbsi sbst sfss sfts sibi sibs siff sift siit sisi siss sist sit- siti sits sitt ssis ssit sssb sssf sssi ssss sstb ssts stbs stib stif stis stit stsf stsi stss tbbs tbit tbst tfsi tfss tibi tibs tiff tift tiit tisb tisi tiss tist titi tits titt tsis tssf tssi tsst tsts ttbb ttff ttss tttt