CREATE TABLE table_name_18 (founded NUMBER, stadium VARCHAR2, club VARCHAR2)

What year was the team Club of atl tico de san juan fc who plays at hiram bithorn stadium founded.
SELECT SUM(founded) FROM table_name_18 WHERE stadium = "hiram bithorn stadium" AND club = "atlético de san juan fc"
SELECT SUM("founded") FROM "table_name_18" WHERE "atlético de san juan fc" = "club" AND "hiram bithorn stadium" = "stadium"