to live separately from their children and grandchildren. This was usually connected to cheating of the propiska system: the grandparents were registered not for the apartment in which they lived but the apartment of their children, to avoid the return of their apartment to the government after their death. Violations of the propiska system within a single city/town were rarely actually punished. Also, Moscow employers were allowed to employ people from the vicinity of Moscow living in a given radius (around ) from Moscow. In theory, it was possible to exchange apartments over mutual agreement between parties. Few people wanted to move from a large city to a smaller one, even with additional money, but the exchange of two flats for one in a larger city was sometimes possible. Also, apartment exchange with money involved was something of a "gray area" bordering on a criminal offence, and there was a real possibility that the participants would be prosecuted as for an economic crime, and real estate agents arranging such things were strictly outlawed and prosecuted, living in a "gray area" and hiding their activities from the authorities. Many people used subterfuge to get a Moscow propiska, including marriages of convenience and bribery. Another way of obtaining Moscow residency was to become a limitchik: to enter Moscow to take certain understaffed job positions, such as at cleaning services, according to a certain workforce quota (limit). Such people were provided with a permanent living place (usually a flat or a room in a shared flat) for free, in exchange for working for a certain number of years. Some valuable specialists, such as scientists or engineers, could also be invited by enterprises, which provided them with flats at the expense of the enterprise. At a certain period, residents of rural areas had their passports stored at selsoviets (officially "for safekeeping") which prevented them from unofficial migration to the areas where they did not have apartments. This was intended to prevent cities from having an influx of migrants who sought higher living standards in large cities but had permanent registration far away from their actual place of residence. Propiska fee in Moscow In the late 1980s and early 1990s, just before the collapse of the USSR, the authorities in Moscow introduced an official charge to be permanently registered in Moscow even in their own property. The fee was around US$5,000, around a quarter of