During the 1940s and 1950s, urbanization accelerated and the built-up area was increased to 68 km2 by 1962, an almost fourteen-fold increase compared to 1925. The Serena Hotel opened in 1945 as the first Western style luxury hotel. Under the premiership of Mohammad Daoud Khan in the 1950s, foreign investment and development increased. In 1955, the Soviet Union forwarded $100 million in credit to Afghanistan, which financed public transportation, airports, a cement factory, mechanized bakery, a five-lane highway from Kabul to the Soviet border and dams, including the Salang Pass to the north of Kabul. During the 1960s, Soviet-style microrayon housing estates were built, containing sixty blocks. The government also built many ministry buildings in the brutalist architecture style. In the 1960s the first Marks & Spencer store in Central Asia was built in the city. Kabul Zoo was inaugurated in 1967, which was maintained with the help of visiting German zoologists. During this time, Kabul experimented with liberalization, notably the loosening of restrictions on speech and assembly which led to student politics in the capital and various demonstrations by Socialist, Maoist, liberal or Islamist factions.