What is the quantity for railway 263?
CREATE TABLE "passenger_and_express_train_locomotives" (
  "class" text,
  "railway_number_s" text,
  "quantity" real,
  "year_s_of_manufacture" text,
  "axle_arrangement" text
);
SELECT "quantity" FROM "passenger_and_express_train_locomotives" WHERE "railway_number_s"='263';