You are given a string, s, consisting of lowercase English letters. Your task is to find the length of the longest self-contained substring of s.

A substring t of s is called self-contained if:

• t is not equal to the entire string s.

• Every character in t does not appear anywhere else in s (outside of t).

In other words, all characters in t are completely unique to that substring within the string s.

Return the length of the longest self-contained substring. If no such substring exists, return -1.

Constraints:

• $2 \leq$ s.length $\leq 1000$

• s consists only of lowercase English letters.