Longest Substring with At Most Two Distinct Characters

You are given a string s. Your task is to find the length of the longest contiguous substring of s that contains at most two distinct characters.

Example:

• For s = "abcbbbbcccbdddadacb", the longest such substring is "bcbbbbccc" with a length of 10.

Note: The substring must be contiguous.

Mathematical Formulation:

Let s be a string and define a substring s[i...j]. Find \[ \max_{0 \le i \le j < n} \{ (j-i+1) \; : \; |\{ s[k] : i \le k \le j \}| \le 2 \}. \]

inputFormat

The input consists of a single line containing the string s. The string may be empty and consists of ASCII characters.

outputFormat

Output a single integer representing the length of the longest substring that contains at most two distinct characters.

abcbbbbcccbdddadacb

10