Given an m x n integer matrix grid, where each cell contains either $0$ (empty) or $1$ (obstacle), you may move one step at a time in any of the four directions (up, down, left, right), but only into empty cells.

Return the minimum number of steps required to travel from the upper-left corner $($0, 0$)$ to the lower-right corner $($m - 1, n - 1$)$, given that you are allowed to eliminate at most k obstacles along the way. If no such path exists, return $-1$.

Constraints:

• m == grid.length

• n == grid[i].length

• $1 \leq$ m, n $\leq 40$

• $1 \leq$ k $\leq$ ...