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Two different aquarium fish shops have special price on Congo Tetra. The price is $42\mathrm{CZK}$ for one fish. Further, the discount of $50\mathrm{CZK}$ from a purchase over $300\mathrm{CZK}$ is offered in shop A. In shop B a customer is given $5\mathrm{\%}$ discount of the price of any purchase. How many of Congo Tetra must one buy to make the total price in shop A lower than the total price in shop B?