Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Examples

Example 1

Input:  s = "leetcode"
Output: 0

The character 'l' at index 0 is the first that does not repeat.

Example 2

Input:  s = "loveleetcode"
Output: 2

Example 3

Input:  s = "aabb"
Output: -1

Constraints

• 1 <= s.length <= 10⁵
• s consists of only lowercase English letters