user: Question: Name the maximum number of disc for Bill Gereghty
Columns: ['No. in series', 'No. Disc', 'Title', 'Directed by', 'Written by', 'Original air date', 'Length (minutes)']
Types: ['text', 'real', 'text', 'text', 'text', 'text', 'real']
Sample row: ['Pilot', 1.0, '" Children of the Gods "', 'Mario Azzopardi', 'Jonathan Glassner & Brad Wright', 'July27,1997 ( Showtime )', 95.0]
SQL:

assistant: SELECT MAX("No. Disc") FROM "Table" WHERE "Directed by" = 'Bill Gereghty';