### Find the Longest Balanced Substring of a Binary String

You are given a binary string `s` consisting only of zeroes and ones.

A substring of `s` is considered balanced if **all zeroes are before ones** and the number of zeroes is equal to the number of ones inside the substring. Notice that the empty substring is considered a balanced substring.

Return *the length of the longest balanced substring of* `s`.

A **substring** is a contiguous sequence of characters within a string.

 

**Example 1:**

```
Input: s = "01000111"
Output: 6
Explanation: The longest balanced substring is "000111", which has length 6.
```

**Example 2:**

```
Input: s = "00111"
Output: 4
Explanation: The longest balanced substring is "0011", which has length 4. 
```

**Example 3:**

```
Input: s = "111"
Output: 0
Explanation: There is no balanced substring except the empty substring, so the answer is 0.
```

 

**Constraints:**

- `1 <= s.length <= 50`
- `'0' <= s[i] <= '1'`

**Function definition**

```
class Solution:
    def findTheLongestBalancedSubstring(self, s: str) -> int:
```

