Name the slope length for 1966 groundstation
CREATE TABLE "skilift_system" (
  "name_or_route" text,
  "type" text,
  "elevation_groundstation" real,
  "elevation_mountainstation" real,
  "slope_length" real,
  "capacity_in_persons_hour" real,
  "construction_year_s" text
);
SELECT COUNT("slope_length") FROM "skilift_system" WHERE "elevation_groundstation"=1966;