Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an n x n integer matrix grid, return the minimum sum of a falling path with non-zero shifts.
A falling path with non-zero shifts is a choice of exactly one element from each row of grid such that no two elements chosen in adjacent rows are in the same column.
 
Please complete the following python code precisely:
```python
class Solution:
    def minFallingPathSum(self, grid: List[List[int]]) -> int:
```