Longest Word Finder

Given a string, you are to extract the longest word from it. A word is defined as a sequence of letters (A–Z, a–z) that may contain at most one apostrophe (') within it. If there are several words with the same length, return the first one encountered. Punctuation and other non-letter characters act as delimiters. The problem requires reading from the standard input and printing the result to the standard output.

Note: If the input is an empty string, output an empty line.

inputFormat

The input consists of a single line containing a sentence. The sentence may include letters, punctuation marks, spaces, and apostrophes.

outputFormat

Output a single line which is the longest word extracted from the sentence following the rules described. If no valid word exists, output an empty line.

Hello world!

Hello