Your mission is to convert the name of a function (a string) from CamelCase ("MyFunctionName") into the Python format ("my_function_name") where all chars are in lowercase and all words are concatenated with an intervening underscore symbol "_".
Input: A function name as a CamelCase string.
Output: The same string, but in under_score.
fromCamelCase('MyFunctionName') == 'my_function_name' fromCamelCase('IPhone') == 'i_phone'
0 < len(string) <= 100
Input data won't contain any numbers.