Russian (, ) is an East Slavic language mainly spoken in Russia. It is the native language of the Russians and belongs to the Indo-European language family. It is one of four living East Slavic languages, and is also a part of the larger Balto-Slavic languages. Besides Russia itself, Russian is an official language in Belarus, Kazakhstan, and Kyrgyzstan, and is used widely as a lingua franca throughout Ukraine, the Caucasus, Central Asia, and to some extent in the Baltic states. It was the de facto language of the former Soviet Union, and continues to be used in public life with varying proficiency in all of the post-Soviet states. Russian has over 258 million total speakers worldwide. It is the most spoken Slavic language, and the most spoken native language in Europe, as well as the most geographically widespread language of Eurasia. It is the world's seventh-most spoken language by number of native speakers, and the world's eighth-most spoken language by total number of speakers. Russian is one of two official languages aboard the International Space Station, as well as one of the six official languages of the United Nations. Russian is written using the Russian alphabet of the Cyrillic script; it distinguishes between consonant phonemes with palatal secondary articulation and those without—the so-called "soft" and "hard" sounds. Almost every consonant has a hard or soft counterpart, and the distinction is a prominent feature of the language. Another important aspect is the reduction of unstressed vowels. Stress, which is often unpredictable, is not normally indicated orthographically, though an optional acute accent may be used to mark stress – such as to distinguish between homographic words (e.g. (, 'lock') and (, 'castle')), or to indicate the proper pronunciation of uncommon words or names. Classification Russian is an East Slavic language of the wider Indo-European family. It is a descendant of Old East Slavic, a language used in Kievan Rus', which was a loose conglomerate of East Slavic tribes from the late 9th to the mid-13th centuries. From the point of view of spoken language, its closest relatives are Ukrainian, Belarusian, and Rusyn, the other three languages in the East Slavic branch. In many places in eastern and southern Ukraine and throughout Belarus, these languages are spoken interchangeably, and in certain areas traditional bilingualism resulted in language mixtures such as Surzhyk in eastern Ukraine and Trasianka in Belarus. An East Slavic Old