Longest Unique Substring

Given a string S consisting of printable characters, find the longest substring of S that contains no repeating characters. If there are multiple substrings with the same maximum length, return the one that appears first in S. The solution must run in \(O(n)\) time complexity, where \(n\) is the length of the string.

Example:

Input: abcabcbb
Output: abc
Input: bbbbb
Output: b
Input: pwwkew
Output: wke

inputFormat

The input consists of a single line containing the string S. The string is provided via standard input (stdin).

outputFormat

Print the longest substring without repeating characters to the standard output (stdout). In the case of a tie, print the substring that appears first in S.## sample

abcabcbb

abc