user: Question: how many times was it the district Illinois 18?
Columns: ['District', 'Incumbent', 'Party', 'First elected', 'Result', 'Candidates']
Types: ['text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Illinois 2', 'Abner J. Mikva', 'Democratic', 1968.0, 'Re-elected', 'Abner J. Mikva (D) 74.7% Harold E. Marks (R) 25.3%']
SQL:

assistant: SELECT COUNT("Candidates") FROM "Table" WHERE "District" = 'Illinois 18';