A train goes from station $\mathrm{A}$ to $\mathrm{D}$ via stations $\mathrm{B}$ and $\mathrm{C}$. The measured distances between various stations are: $\mathrm{A}$ to $\mathrm{B}=648 \mathrm{km}, \mathrm{B}$ to $\mathrm{C}=64.8 \mathrm{km}, \mathrm{C}$ to $\mathrm{D}=6.48 \mathrm{km}$. Total distance covered by the train in proper significant figures is _______ km.