You are asked to cut off all the trees in a forest for a golf event. The forest is represented as an `m x n` matrix. In this matrix:

- `0` means the cell cannot be walked through.
- `1` represents an empty cell that can be walked through.
- A number greater than `1` represents a tree in a cell that can be walked through, and this number is the tree's height.

In one step, you can walk in any of the four directions: north, east, south, and west. If you are standing in a cell with a tree, you can choose whether to cut it off.

You must cut off the trees in order from shortest to tallest. When you cut off a tree, the value at its cell becomes `1` (an empty cell).

Starting from the point `(0, 0)`, return the minimum steps you need to walk to cut off all the trees. If you cannot cut off all the trees, return `-1`.

You are guaranteed that no two trees have the same height, and there is at least one tree needs to be cut off.

Example 1:

    Input: forest = [[1,2,3],[0,0,4],[7,6,5]]
    Output: 6
    Explanation: Following the path above allows you to cut off the trees from shortest to tallest in 6 steps.

Example 2:

    Input: forest = [[1,2,3],[0,0,0],[7,6,5]]
    Output: -1
    Explanation: The trees in the bottom row cannot be accessed as the middle row is blocked.

Example 3:

    Input: forest = [[2,3,4],[0,0,5],[8,7,6]]
    Output: 6
    Explanation: You can follow the same path as Example 1 to cut off all the trees.
    Note that you can cut off the first tree at (0, 0) before making any steps.

Constraints:

- `m == forest.length`
- `n == forest[i].length`
- `1 <= m, n <= 50`
- `0 <= forest[i][j] <= 109`