Razin's parents were from the village of Usman Sobakina, 8 kilometres  outside of Voronezh. He was first noted by history in 1661, as part of a diplomatic mission from the Don Cossacks to the Kalmyks. That same year Razin went on a long-distance pilgrimage to the great Solovetsky Monastery on the White Sea for the benefit of his soul. After that, all trace of him was lost for six years, when he reappeared as the leader of a robber community established at Panshinskoye, among the marshes between the rivers Tishina and Ilovlya, from whence he levied tribute from all vessels passing up and down the Volga. A long war with Poland in 1654-1667 and Sweden in 1656-1658 put heavy demands upon the people of Russia. Taxes increased, as did conscription. Many peasants, hoping to escape these burdens, fled south and joined bands of Razin's marauding Cossacks. They were also joined by many others who were disaffected with the Russian government, including people of the lower classes, as well as representatives of non-Russian ethnic groups such as Kalmyks, that were being oppressed at the time. Razin's first considerable exploit was to destroy the great naval convoy consisting of the treasury barges and the barges of the Patriarch and the wealthy merchants of Moscow. Razin then sailed down the Volga with a fleet of 35 vessels, capturing the more important forts on his way and devastating the country. At the beginning of 1668, he defeated the voivode Yakov Bezobrazov, sent against him from Astrakhan, and in the spring embarked on a predatory expedition into Daghestan and Persia, which lasted for eighteen months.
Question: How long did Razin's expedition last?
Answer: eighteen months.