Find Most Frequent Letters

Given a string, find all the alphabetic characters (letters) that occur most frequently. Letters are considered case-sensitively, meaning that 'A' and 'a' are treated as different characters.

If the string contains no letters, output an empty line. When multiple letters tie for the highest frequency, output each of them in the order of their first appearance in the input.

inputFormat

The input is read from standard input. It consists of a single line containing a string, which may include spaces, punctuation, digits, etc.

outputFormat

Output to standard output the most frequent letter(s) separated by a single space. If there are no letters, output an empty line.## sample

Hello World!

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