First Unique Character in a String

You are given a string S consisting only of lowercase English letters. Your task is to find the index \( i \) of the first character in S that occurs exactly once. If there is no such character, output \( -1 \).

More formally, let S be a string of length \( n \). You need to find the smallest index \( i \) (0-indexed) such that the frequency of S[i] in \( S \) is 1. If no such \( i \) exists, return \( -1 \).

Example:

Input:  leetcode
Output: 0
Explanation: 'l' occurs only once and is the first unique character in "leetcode".

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inputFormat

The input consists of a single line containing the string S, where \( 1 \leq |S| \leq 10^5 \) and each character of S is a lowercase English letter.

outputFormat

Output a single integer representing the index of the first non-repeating character in S. If there is no such character, output \( -1 \).

## sample

leetcode

0

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