A monitoring script scans a raw log token — a single string made only of lowercase English letters — looking for the first character that was logged exactly once.
Given the token, find the leftmost character that appears exactly once in it. Print that character. If every character repeats (no character appears exactly once), print NONE.
Input format
Line 1: a string s consisting only of lowercase English letters (a-z).
Output format
A single line containing the first (leftmost) character of s that occurs exactly once in s, or the literal text NONE if no such character exists.
Constraints
- 1 ≤ length(s) ≤ 100000
scontains only lowercase English letters.