# Minimum path sum in matrix

## Question

Given a matrix M, **write a function to find the minimum sum of all numbers encountered on the path moving from the top left to the bottom right of the matrix**. You are only allowed to move down or to the right at each step, and your matrix will be filled with non-negative numbers.

For example:

```
M = [[1, 2, 3],
[4, 1, 2],
[1, 5, 3]]
# Returns 9 because we go from 1 -> 2 -> 1 -> 2 -> 3 = 9
```