The time taken to reach a high level of proficiency can vary depending on the language learned. In the case of native English speakers, some estimates were provided by the Foreign Service Institute (FSI) of the U.S. Department of State, which compiled approximate learning expectations for a number of languages for their professional staff (native English speakers who generally already know other languages). Of the 63 languages analyzed, the five most difficult languages to reach proficiency in speaking and reading, requiring 88 weeks (2200 class hours), are Arabic, Cantonese, Mandarin, Japanese and Korean.