 Karadžić based his alphabet on the previous "Slavonic-Serbian" script, following the principle of ""write as you speak and read as it is written"", removing obsolete letters and letters representing iotified vowels, introducing from the Latin alphabet instead, and adding several consonant letters for sounds specific to Serbian phonology.During the same period, Croatian linguists led by Ljudevit Gaj adapted the Latin alphabet, in use in western South Slavic areas, using the same principles.As a result of this joint effort, Cyrillic and Latin alphabets for Serbo-Croatian have a complete one-to-one congruence, with the Latin digraphs Lj, Nj, and Dž counting as single letters.