auto created java class start with number in some dmoj questions

[TTMathCS]

Steps to reproduce the issue:

1. in Chrome go to dmoj question, https://dmoj.ca/problem/coci19c3p1, click on the green plus ("competitive companion" for Chrome), then in VS code it prompt to select language.
2. In VS Code, select java as the language, then file "1_Preokret.java" is automatically created.

The issue is that: The first character cannot be number, and it needs to be a "Java letter", which includes letters, underscore and dollar sign. ( https://docs.oracle.com/javase/specs/jls/se7/html/jls-3.html#jls-3.8)

I tried to rename it to COCI_1_Parking.java, and updated the name in the prob file. But extension didn't work, My guess is that the hash cannot be verified? (.1_Preokret.java_28e54445d12ea9556b3944e653d7e248.prob)

I am not sure if this is an issue, or I just I didn't use the extension in the right way? Thank you!