Common Characters Finder

You are given two strings. Your task is to find the unique set of characters that occur in both strings. The comparison is case-insensitive, and only alphabetical characters (a-z, A-Z) are considered.

If either string is empty or has more than \(100\) characters, you should output "invalid input".

The resulting common characters must be output in sorted order.

Example:

Input:
Hello
world
Output:
["l", "o"]

</p>

inputFormat

The input is provided via standard input (stdin) and consists of two lines. The first line contains the first string, and the second line contains the second string.

outputFormat

If both input strings are valid (non-empty and no longer than 100 characters), output the sorted list of common alphabetical characters in Python list style (e.g., ["a", "b", "c"]). Otherwise, output the string "invalid input".

## sample

Hello
world

["l", "o"]