Longest Substring with At Most Two Distinct Characters

Given a string s, find the length of the longest contiguous substring that contains at most two distinct characters. In other words, for a substring s[i...j], it must satisfy that the number of unique characters in it is at most 2. Formally, if we denote by \(\#distinct(s[i...j])\) the number of distinct characters in the substring, then we require:

[ #distinct(s[i...j]) \le 2 ]

Your task is to compute the maximum \(j-i+1\) among all valid substrings. For example, if s = "eceba", one of the longest valid substrings is "ece" with a length of 3.

inputFormat

The input consists of a single line containing the string s.

You should read the input from stdin.

outputFormat

Output a single integer which is the length of the longest substring of s that contains at most two distinct characters. Write the output to stdout.

eceba

3