First Unique Character in a String

Given a string `s`, find the first non-repeating character in it and return its index. If it does not exist, return `-1`. ### Constraints - `1 <= s.length <= 10^5` - `s` consists of only lowercase English letters. ### Input Format A single line containing the string `s`. ### Output Format Print the 0-based index of the first unique character, or `-1` if none exists.