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, at most `k` times.
Return *the length of the longest substring containing the same letter you can get after performing the above operations*.
Example 1
Input: s = "ABAB", k = 2
Output: 4
Explanation: Replace the two 'A's with two 'B's or vice versa.
Example 2
Input: s = "AABABBA", k = 1
Output: 4
Explanation: Replace the one 'A' in the middle with 'B' and form "ABBB".