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

You are given a string s and an integer k. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most k times.
Return the length of the longest substring containing the same letter you can get after performing the above operations.
 
Please complete the following python code precisely:
```python
class Solution:
    def characterReplacement(self, s: str, k: int) -> int:
```