Most Frequent Character

You are given a string s. Your task is to determine the most frequent alphabetic character in the string. The character count is case‐insensitive and non-alphabetic characters are ignored. In case of a tie (i.e., two or more characters having the same highest frequency), output the character that appears first in the string (when the string is converted to lower-case).

For example, given the string aabbcc, the characters 'a', 'b', and 'c' all appear twice, but 'a' appears first, so the output should be a.

If the string is empty or has no alphabetic characters, output an empty string.

In mathematical terms, if we let \( f(c) \) be the frequency of character \( c \) (considering \( c \) in lowercase), then the result is the first character \( c \) in the order of appearance in \( s \) such that \( f(c) = \max\{f(x): x \in \text{alphabetic characters in } s\} \).

inputFormat

The input consists of a single line string s. The string may contain spaces, punctuation, or other non-alphabetic characters. Input is read from standard input (stdin).

outputFormat

Output a single character — the most frequent alphabetic character in lowercase. If no alphabetic character exists, output an empty string. Output should be written to standard output (stdout).

aabbcc

a