The health sector comprises 17 specialized hospitals and centers, 4 regional diagnostic and treatment centers, 9 district and 21 aimag general hospitals, 323 soum hospitals, 18 feldsher posts, 233 family group practices, 536 private hospitals, and 57 drug supply companies/pharmacies. In 2002, the total number of health workers was 33,273, of whom 6823 were doctors, 788 pharmacists, 7802 nurses, and 14,091 mid-level personnel. At present, there are 27.7 physicians and 75.7 hospital beds per 10,000 inhabitants.. How many districts and aimag general hospitals does the health sector comprise of?