CREATE TABLE table_name_50 (fa_cup INTEGER, total VARCHAR(255), fa_trophy VARCHAR(255), club VARCHAR(255))
What is the sum of FA cups of club Stalybridge Celtic, which has more than 0 FA trophies and a total less than 20?
    
SQL: SELECT SUM(fa_cup) FROM table_name_50 WHERE fa_trophy > 0 AND club = "stalybridge celtic" AND total < 20