Tell me the total number of crest length for year construction larger than 1957 for mattmark
CREATE TABLE "see_also" (
  "name" text,
  "canton" text,
  "height_meters" real,
  "crest_length_meters" real,
  "type" text,
  "year_of_construction" real,
  "name_of_the_lake" text
);
SELECT COUNT("crest_length_meters") FROM "see_also" WHERE "year_of_construction">1957 AND "name"='mattmark';