Instructions: In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.
Input: Passage: In 1903, the party split into Bolsheviks led by Vladimir Lenin and Mensheviks led by Julius Martov and Lunacharsky sided with the former. In 1907, he attended the International Socialist Congress, held in Stuttgart. When the Bolsheviks in turn split into Lenin's supporters and Alexander Bogdanov's followers in 1908, Lunacharsky supported his brother-in-law Bogdanov in setting up Vpered. Like many contemporary socialists (including Bogdanov), Lunacharsky was influenced by the empirio-criticism philosophy of Ernst Mach and Avenarius. Lenin opposed Machism as a form of subjective idealism and strongly criticised its proponents in his book Materialism and Empirio-criticism (1908). In 1909, Lunacharsky joined Bogdanov and Gorky at the latter's villa on the island of Capri, where they started a school for Russian socialist workers. In 1910, Bogdanov, Lunacharsky, Mikhail Pokrovsky and their supporters moved the school to Bologna, where they continued teaching classes through 1911. In 1913, Lunacharsky moved to Paris, where he started his own Circle of Proletarian Culture.
Link Information: Its urban area has a population of 634,830 Answer: 634,830
Output:
What is the population of the city which hosted the socialist congress Lunacharsky attended in 1907?