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

The appeal of a string is the number of distinct characters found in the string.

For example, the appeal of "abbca" is 3 because it has 3 distinct characters: 'a', 'b', and 'c'.

Given a string s, return the total appeal of all of its substrings.
A substring is a contiguous sequence of characters within a string.
 
Please complete the following python code precisely:
```python
class Solution:
    def appealSum(self, s: str) -> int:
```