Common Characters Finder

Given two strings, your task is to find all unique characters that appear in both strings. The matching is case-insensitive, and the result should be output in lowercase in sorted order.

Formally, let \( s_1 \) and \( s_2 \) be two input strings. Define the set of common characters as follows:

\[ C = \{ c \mid c \in \text{toLower}(s_1) \text{ and } c \in \text{toLower}(s_2) \} \]

You should output the characters in \( C \) as a single string with the characters in ascending order. If there are no common characters, output an empty line.

Example:

Input:
abc
cab
Output:
abc

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inputFormat

The input consists of two lines:

1. The first line contains the string \( s_1 \).
2. The second line contains the string \( s_2 \).

Both strings may include letters, numbers, spaces, and punctuation.

outputFormat

Output a single line containing a sorted string of unique lowercase characters that appear in both input strings. If there are no common characters, output an empty line.

## sample

abc
cab

abc

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