user: Question: Who was the President of Czechoslovakia when an ambassador's tenure began in 1950?
Columns: ['Name', 'Tenure Begin', 'Tenure End', 'British monarch', 'Czechoslovak president']
Types: ['text', 'text', 'real', 'text', 'text']
Sample row: ['Sir George Clerk', '1919', 1926.0, 'George V', 'Tomáš Garrigue Masaryk']
SQL:

assistant: SELECT "Czechoslovak president" FROM "Table" WHERE "Tenure Begin" = '1950';