When yidu 宜都 is the commandery what is the lowest number of countries?
CREATE TABLE "territories_of_eastern_wu" (
  "province" text,
  "provincial_capital" text,
  "commandery" text,
  "commandery_capital" text,
  "no_of_counties" real
);
SELECT MIN("no_of_counties") FROM "territories_of_eastern_wu" WHERE "commandery"='Yidu 宜都';