fff ffn ffo ffs fft fnf fnn fns fnt fof fon foo fos fot fsf fsn fso fss fst ftf ftn fto fts ftt nff nfn nfo nfs nft nnf nnn nno nns nnt no- nof non noo nos not nsf nsn nso nss nst ntf ntn nto nts ntt of- off ofn ofo ofs oft on- onf onn ono ons ont oo- oof oon ooo oos oot os- osf osn oso oss ost ot- otf otn oto ots ott sff sfn sfo sfs sft snf snn sno sns snt sof son soo sos sot ss- ssf ssn sso sss sst stf stn sto sts stt tff tfn tfo tfs tft tnf tnn tno tns tnt to- tof ton too tos tot tsf tsn tso tss tst ttf ttn tto tts ttt