SELECT MIN("Goals for") FROM table_68170 WHERE "Wins" = '18' AND "Goals against" < '38'
What is the smallest number of 'goals for' out of the clubs where there were 18 wins and fewer than 38 'goals against'?
CREATE TABLE table_68170 (
    "Position" real,
    "Club" text,
    "Played" real,
    "Points" text,
    "Wins" real,
    "Draws" real,
    "Losses" real,
    "Goals for" real,
    "Goals against" real,
    "Goal Difference" real
)