Most Frequent Character

You are given a string s and your task is to determine the character that appears most frequently in the string. In the event of a tie (i.e. multiple characters having the same frequency), the answer is the character that appears first in the string.

If the input string is empty, output None.

You may refer to the frequency formula: \( f(c) = \#\{ i \mid s_i = c \} \).

inputFormat

The input consists of a single line containing the string s.

outputFormat

Output a single line representing the most frequent character based on the criteria above. If the string is empty, output None.

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