$${\rho = \frac{1,67 \times 10^{-27}\, \mathrm{kg}}{\frac{4}{3} \pi (1,2 \times 10^{-15}\, \mathrm{m})^3} \approx \underline{\underline{2 \times 10^{17}\, \mathrm{kg/m^3}}}}$$