$50$
5. It is known that newly mined iron ore mainly contains iron and other impurities, and the smelting process is actually the removal of other impurities. Now there is a 1000 kilogram piece of iron ore, containing $5.95 \%$ impurities, which, after smelting, becomes an iron block with an iron content of $99 \%$. Then, the smelting process removed $\qquad$ kilograms of impurities. (Neglect any loss of iron)