user: Question: For how many years combined were frank gifford and dan dierdorf color commentators?
Columns: ['Year', 'Network', 'Play-by-play', 'Color commentator(s)', 'Sideline reporter(s)']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1990.0, 'ESPN', 'Mike Patrick', 'Joe Theismann', 'Chris Berman']
SQL:

assistant: SELECT COUNT("Year") FROM "Table" WHERE "Color commentator(s)" = 'frank gifford and dan dierdorf';