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

You are given two strings s and t consisting of only lowercase English letters.
Return the minimum number of characters that need to be appended to the end of s so that t becomes a subsequence of s.
A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.
 
Please complete the following python code precisely:
```python
class Solution:
    def appendCharacters(self, s: str, t: str) -> int:
```