user: Question: what is the minimum stage where mountains classification is Aitor Osa and Aitor González won?
Columns: ['Stage', 'Winner', 'General classification', 'Points classification', 'Mountains classification', 'Combination classification', 'Team classification']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, 'ONCE-Eroski', 'Joseba Beloki', 'no award', 'no award', 'Joseba Beloki', 'ONCE-Eroski']
SQL:

assistant: SELECT MIN("Stage") FROM "Table" WHERE "Mountains classification" = 'Aitor Osa' AND "Winner" = 'Aitor González';