Write a function `max_of_nth(matrix, n)` that takes a matrix represented as a list of lists and an integer `n`, and returns the maximum value in the `n`th column of the matrix. Assume that the matrix is well-formed (all rows have the same number of columns) and that `n` is a valid column index.
#### Example Usage
```python [main.nopy]
matrix = [
[5, 6, 7],
[1, 3, 5],
[8, 9, 19]
]
print(max_of_nth(matrix, 2)) # Output: 19
matrix = [
[6, 7, 8],
[2, 4, 6],
[9, 10, 20]
]
print(max_of_nth(matrix, 1)) # Output: 10
```