For the 1967 Cleveland Browns season what is the total number of times they played the Minnesota Vikings and had an atttendance smaller than 68,431?
CREATE TABLE "schedule" (
  "week" real,
  "date" text,
  "opponent" text,
  "result" text,
  "attendance" real
);
SELECT COUNT("week") FROM "schedule" WHERE "opponent"='minnesota vikings' AND "attendance"<'68,431';