Given a string `s`

and an integer `k`

, return *the length of the longest substring of* `s`

*such that the frequency of each character in this substring is greater than or equal to* `k`

.

**Example 1:**

Input:s = "aaabb", k = 3Output:3Explanation:The longest substring is "aaa", as 'a' is repeated 3 times.

**Example 2:**

Input:s = "ababbc", k = 2Output:5Explanation:The longest substring is "ababb", as 'a' is repeated 2 times and 'b' is repeated 3 times.

**Constraints:**

`1 <= s.length <= 10`

^{4}`s`

consists of only lowercase English letters.`1 <= k <= 10`

^{5}

class Solution {
public int longestSubstring(String s, int k) {
}
}