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

There is a country of n cities numbered from 0 to n - 1. In this country, there is a road connecting every pair of cities.
There are m friends numbered from 0 to m - 1 who are traveling through the country. Each one of them will take a path consisting of some cities. Each path is represented by an integer array that contains the visited cities in order. The path may contain a city more than once, but the same city will not be listed consecutively.
Given an integer n and a 2D integer array paths where paths[i] is an integer array representing the path of the ith friend, return the length of the longest common subpath that is shared by every friend's path, or 0 if there is no common subpath at all.
A subpath of a path is a contiguous sequence of cities within that path.
 
Please complete the following python code precisely:
```python
class Solution:
    def longestCommonSubpath(self, n: int, paths: List[List[int]]) -> int:
```