53*. The King has traversed a $9 \times 9$ board, visiting each of its squares exactly once. The King's route is not closed and may be self-intersecting. What is the maximum possible length of such a route, if the length of a diagonal move is $\sqrt{2}$, and the length of a vertical or horizontal move is 1?

## 10th grade
86.53. Answer. $16+64 \sqrt{2}$.