Given a string s consisting of lowercase English letters, find the length of the longest substring in which every character that appears does so an even number of times. Return the length of that substring. The substring must be contiguous. Example: s = "abacbc", the longest substring where every character appears an even number of times is "bacb" (characters: b,a,c,b -> a appears once? wait), so adjust example properly.
("abacbc")4