def rem_num_of_lines(in_filename, start_string):
    """
    Returns the number of lines that is remaining in the given file starting
    from the first appearance of the given start string.
    ---------
    PARAMETERS:
    <in_filename> Input filename

    <start_string> Start string to be search in <in_file>.

    ---------
    RETURNS:
    <lines_rem> Number of lines remaining in <in_file> after the first
    appearance of <start_string>, includes the line where <start_string> first
    appeared in the count.
    """
    lines_rem = 0
    start_string_found = False
    with open(in_filename) as in_file:
        for line in in_file:
            if not start_string_found:
                if start_string in line:
                    start_string_found = True
            if start_string_found is True:
                lines_rem += 1
    return lines_rem