Sed Passwords

The notorious hacker group "Sed" managed to obtain a string $S$ from their secret sources. The string contains only lowercase English letters along with the character '?'. A substring of $S$ is a contiguous subsequence of that string. For example, the string "chef" is a substring of the string "codechef", but the string "codeh" is not a substring of "codechef". A substring of $S$ is *good* i