Longest Substring with Equal Number of 'a's and 'b's

Given a string s consisting solely of the characters 'a' and 'b', your task is to find the length of the longest contiguous substring that contains an equal number of 'a's and 'b's.

More formally, let \( S \) be the given string. You need to determine the maximum length \( L \) for which there exists a substring \( S[i \ldots j] \) such that:

[ #a(S[i \ldots j]) = #b(S[i \ldots j]) ]

Input Constraints: The input string will contain at least one character and will only consist of the letters 'a' and 'b'.

Your algorithm should be efficient to handle large strings.

inputFormat

The input consists of a single line containing a non-empty string s made up of only 'a' and 'b' characters.

outputFormat

Output a single integer which is the length of the longest contiguous substring of s that contains an equal number of 'a's and 'b's.

abba

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