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

Given an alphanumeric string s, return the second largest numerical digit that appears in s, or -1 if it does not exist.
An alphanumeric string is a string consisting of lowercase English letters and digits.
 
Please complete the following python code precisely:
```python
class Solution:
    def secondHighest(self, s: str) -> int:
```