Which season was there a game with the score of 1:3 played at the venue of national stadium, maldives?
CREATE TABLE "results" (
  "season" real,
  "team_1" text,
  "score" text,
  "team_2" text,
  "venue" text
);
SELECT SUM("season") FROM "results" WHERE "score"='1:3' AND "venue"='national stadium, maldives';