user: Question: What is the lowest Year, when Lok Sabha is "4th Lok Sabha"?
Columns: ['Year', 'Lok Sabha', 'Members of Parliament', 'Party Won', "Winner's % votes", 'Trailing Party', 'Trailing Party % votes']
Types: ['real', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: [1951.0, '1st Lok Sabha', 'Mukund Lal Agrawal', 'Indian National Congress', '43.11%', 'Socialist Party', '22.58%']
SQL:

assistant: SELECT MIN("Year") FROM "Table" WHERE "Lok Sabha" = '4th Lok Sabha';