Given a `m x n` `grid` filled with non-negative numbers, find a path from top left to bottom right, which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

Example 1:

    Input: grid = [[1,3,1],[1,5,1],[4,2,1]]
    Output: 7
    Explanation: Because the path 1 → 3 → 1 → 1 → 1 minimizes the sum.

Example 2:

    Input: grid = [[1,2,3],[4,5,6]]
    Output: 12

Constraints:

- `m == grid.length`
- `n == grid[i].length`
- `1 <= m, n <= 200`
- `0 <= grid[i][j] <= 100`