import re


def keep_e(st):
    """
    Takes in string, returns that string with all letters that
    are not e's changed to (NOT_E).
    "Hello" -> "(NOT_E)e(NOT_E)(NOT_E)(NOT_E)"
    """
    return re.sub(r"[A-D | F-Z | a-d | f-z]", "(NOT_E)", st)