Longest Unique Substring

Given a string S, your task is to determine the length of the longest substring that contains only unique characters. In other words, find the maximum length of a contiguous segment of S where no character repeats.

This is a classic problem that can be efficiently solved using the sliding window technique in O(n) time complexity, where n is the length of the string. Understanding how to update the window correctly when a repeated character is encountered is key to solving this problem.

inputFormat

The input consists of a single line containing the string S. Note that S may contain letters, digits, and special characters, and it can also be empty.

outputFormat

Output a single integer representing the length of the longest substring in S that does not contain any repeating characters.

## sample

abcabcbb

3